Allowance for Credit Losses - Accrued Interest Receivables (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	$ 264
Allowance for credit losses	2
Accrued interest receivables, net	262
Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	140
Charge-off of accrued interest receivables	7
Securities Held-to-maturity [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	23
Other Financial Assets Measured at Amortized Cost [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	1
Securities available-for-sale [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	$ 100