Allowance for Credit Losses - Accrued Interest Receivables (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	$ 248		$ 264
Allowance for credit losses	2		2
Accrued interest receivables, net	246		262
Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	137		140
Charge-off of accrued interest receivables	0	$ 1
Securities Held-to-maturity [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	20		23
Other Financial Assets Measured at Amortized Cost [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	1		1
Securities available-for-sale [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	$ 90		$ 100