Allowance for Credit Losses - Accrued Interest Receivables (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	$ 283	$ 283
Allowance for credit losses	2	2
Accrued interest receivables, net	281	281
Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	152	152
Charge-off of accrued interest receivables	1	5
Securities Held-to-maturity [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Total accrued interest receivables	26	26
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	$ 104	$ 104