Add docs on cost management (#5480)

* Gain root access to AWS account

* Add note on multi-year cost explorer

docs/topic/access-creds/cloud-auth.md

@@ -116,6 +116,20 @@ To do so, follow these steps:
    AWS accounts we create.
 4. Create the account! They'll receive an email with appropriate instructions.
 
+#### Gain root access to an AWS account
+
+In some cases we need to gain root access to an AWS account, e.g. migrating billing responsibility to a client. To do this,
+
+1. Log into the AWS SSO and take note of the Account ID (12 digits) and root user email address that you want to gain root access to. This information is also available by viewing "Organizations" from the [2i2c-sandbox account](https://us-east-1.console.aws.amazon.com/organizations/v2/home/accounts). The root user email address is usually aliased to `[email protected]`.
+1. Sign into AWS and click on {bdg-muted-line}`Sign in using root user email`.
+1. Enter the root user email address and click on {bdg-muted-line}`Next`.
+1. Click on {bdg-muted-line}`Forgot password`.
+1. Complete the CAPTCHA to send a password reset request to the root user email address.
+1. Follow the instructions to reset the password.
+1. Sign in using the root user email address and the new password. You will be prompted to enter a verification code sent to the root user email address.
+
+You should now have root access to the AWS account.
+
 (cloud-access:aws-individual-accounts)=
 ### Access individual AWS accounts
 

docs/topic/billing/reports.md

@@ -39,6 +39,10 @@ This provides 'Monthly costs by linked account' and 'Monthly costs by
 service'. Once you open those reports, you can further filter and group
 as you wish. A CSV of reports can also be downloaded from this page.
 
+#### Enable multi-year cost explorer data
+
+Multi-year data is not available by default in the AWS Cost Explorer. To enable it, log into the {ref}`2i2c management account<cloud-access:aws-sso>` via the SSO and follow the AWS User Guide on [Configuring multi-year and granular data](https://docs.aws.amazon.com/cost-management/latest/userguide/ce-configuring-data.html).
+
 ### Azure
 
 We have limited expertise here, as we have never actually had billing