Loans and Allowance for Credit Losses: Loans and Unfunded Credit Commitments - Allowance for Credit Losses: Unfunded Credit Commitments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Financing Receivable, Allowance for Credit Loss [Line Items]
Change in allowance for credit loss	$ (1)
Allowance for credit loss, beginning balance	422	$ 448
Provision for (reduction in) credit losses	8	34
Allowance for credit loss, ending balance	421	392
Unfunded Credit Commitments
Financing Receivable, Allowance for Credit Loss [Line Items]
Change in allowance for credit loss	4
Allowance for credit loss, beginning balance	171	121
Provision for (reduction in) credit losses	4	(16)
Allowance for credit loss, ending balance	$ 175	$ 105