Basis of Presentation - Narrative (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Jan. 01, 2020	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative effect of change in accounting principles			$ 279,354	$ 261,330	$ 256,515
Fair value gains as a result of measurement alternative			167	243
Cumulative effect of change in accounting principles
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Decrease to retained earnings due to CECL adoption	$ 2,700
Other assets | Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value gains as a result of measurement alternative		$ 505		201	149
Retained earnings
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative effect of change in accounting principles			236,990	223,211	199,202	$ (183)	$ 177,676
Retained earnings | Cumulative effect of change in accounting principles
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative effect of change in accounting principles				(2,650)	62		(183)
AOCI
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative effect of change in accounting principles			$ 7,986	$ 1,569	$ (1,507)	$ 88	(119)
AOCI | Cumulative effect of change in accounting principles
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative effect of change in accounting principles							$ 88