Accounting Policies - Impact of CECL Standard Adoption (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan and lease losses		$ 5,361	$ 2,742	$ 2,629	$ 2,611
Unfunded lending related commitments		584	318
Other
Total allowance for credit losses			3,060
Retained earnings		46,848	42,215
Income taxes from continuing operations		426	901	928
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan and lease losses	$ 463		463
Unfunded lending related commitments	179		179
Other	19
Total allowance for credit losses	661
Retained earnings	(671)
Fair value - assets	200
Income taxes from continuing operations	200
Cumulative Effect, Period of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan and lease losses	3,205		3,205
Unfunded lending related commitments	497		497
Other	19
Total allowance for credit losses	3,721
Retained earnings	41,544
Total commercial lending
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan and lease losses		3,337	1,812	1,663	1,582
Unfunded lending related commitments		485	316
Total commercial lending | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan and lease losses	(304)		(304)
Unfunded lending related commitments			53
Total commercial lending | Cumulative Effect, Period of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan and lease losses	1,508		1,508
Unfunded lending related commitments			369
Total consumer lending
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan and lease losses		2,024	930	$ 966	$ 1,029
Unfunded lending related commitments		$ 99	2
Total consumer lending | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan and lease losses	767		767
Unfunded lending related commitments			126
Total consumer lending | Cumulative Effect, Period of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan and lease losses	$ 1,697		1,697
Unfunded lending related commitments			$ 128