Investment Securities (Narrative) (Details) - USD ($) $ in Millions		Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019
Schedule of Investments [Line Items]
Held-to-maturity debt securities, allowance for credit loss		$ 2
Available for sale debt securities, amortized cost		86,224		$ 67,790
Available-for-sale securities, fair value		89,077		69,163
Investment securities, net unsettled investment purchases		388			$ 623
Held-to-maturity securities, amortized cost	[1]	1,469		17,661
Held-to-maturity securities, fair value		1,621		$ 18,044
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Investments [Line Items]
Debt securities amortized cost amount of debt securities exceeds 10 percent of shareholders equity		38,600
Fair value of debt securities of a single issuer that exceeeds 10 percent of shareholders equity		40,000
Federal Home Loan Mortgage Corporation (FHLMC) Insured Loans [Member]
Schedule of Investments [Line Items]
Debt securities amortized cost amount of debt securities exceeds 10 percent of shareholders equity		7,100
Fair value of debt securities of a single issuer that exceeeds 10 percent of shareholders equity		$ 7,300
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2019-04 [Member]
Schedule of Investments [Line Items]
Available for sale debt securities, amortized cost			$ 16,200
Available-for-sale securities, fair value			16,500
Held-to-maturity securities, amortized cost			(16,200)
Held-to-maturity securities, fair value			$ (16,500)

[1] Amounts as of March 31, 2020 are net of the related Allowances for Credit Losses recorded in accordance with the adoption of Accounting Standards Update 2016-13, Financial Instruments - Credit Losses, which totaled $2 million and $19 million for Investment securities and Other assets, respectively. See Recently Adopted Accounting Standards portion of Note 1 Accounting Policies for additional detail on the adoption of this ASU.