Investment Securities (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Investment securities, allowance for credit loss	$ 82
Provision for credit losses on investment securities	80
Securities available for sale debt securities, amortized cost	84,172			$ 67,790
Investment securities – available for sale	87,358			69,163
Investment securities – held to maturity	1,441			17,661
Held-to-maturity securities, fair value	1,605			18,044
Net unsettled investment purchases	200			500
Cumulative Effect, Period of Adoption, Adjustment
Schedule of Investments [Line Items]
Securities available for sale debt securities, amortized cost		$ 49	$ 16,200	16,200
Investment securities – available for sale		48	$ 16,500	16,500
Investment securities – held to maturity		(49)		(16,200)
Held-to-maturity securities, fair value		$ (48)		$ (16,500)
Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Investments [Line Items]
Amortized cost of debt securities of a single issuer that exceeds 10 percent of shareholders equity	32,900
Fair value of debt securities of a single issuer that exceeds 10 percent of shareholders equity	34,200
Federal Home Loan Mortgage Corp (FHLMC)
Schedule of Investments [Line Items]
Amortized cost of debt securities of a single issuer that exceeds 10 percent of shareholders equity	14,700
Fair value of debt securities of a single issuer that exceeds 10 percent of shareholders equity	$ 14,900