Accounting Policies (Details) - USD ($) $ in Millions			3 Months Ended
		Jan. 01, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings			$ (41,885)		$ (42,215)
Investment securities – held to maturity (b)	[1]		1,469		17,661
Held-to-maturity securities, fair value			1,621		18,044
Other comprehensive income (loss), before tax and net of reclassifications into Net income			2,251	$ 927
Available for sale debt securities, amortized cost			86,224		67,790
Investment securities – available for sale			$ 89,077		$ 69,163
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings		$ 671
Accounting Standards Update 2019-04 [Member] | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment securities – held to maturity (b)		(16,200)
Held-to-maturity securities, fair value		(16,500)
Other comprehensive income (loss), before tax and net of reclassifications into Net income		306
Available for sale debt securities, amortized cost		16,200
Investment securities – available for sale		$ 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.