Fair Value Measurement and Fair Value of Financial Instruments - Reconciliation of Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, end of period	$ 1		$ 1
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Settlements		$ 14
Trading derivatives
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	(1)	(3)		$ (8)
Included in income before taxes	0	0		(3)
Included in other comprehensive income	0	0		0
Purchases/additions	0	0		0
Settlements	0	1		3
Asset (liability) balance, end of period	(1)	(2)	(1)	(2)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	0	0		3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfers, Net	0		0	0
Other Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	(3)	(124)	(4)	(124)
Included in income before taxes	4	(2)	3	(2)
Included in other comprehensive income	0	0	0	0
Purchases/additions	0	0	0	0
Settlements	0		0	14
Asset (liability) balance, end of period	(7)	(108)	(7)	(108)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	(4)	1	(3)	1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfers, Net	0		0	0
Trading Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period			(1)
Included in income before taxes			0
Included in other comprehensive income			0
Purchases/additions			0
Settlements			0
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period			0
Trading derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	1	3		8
Included in income before taxes	0	0		(3)
Included in other comprehensive income	0	0		0
Purchases/additions	0	0		0
Settlements	0	(1)		(3)
Asset (liability) balance, end of period	1	2	1	2
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	0	0		(3)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net				0
Securities Available for Sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	1,364	1,123	1,474	1,131
Included in income before taxes	0	0	0	0
Included in other comprehensive income	31	4	(11)	1
Purchases/additions	1	29	44	30
Settlements	(152)	(31)	(263)	(37)
Asset (liability) balance, end of period	1,244	1,125	1,244	1,125
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	0	0	0	0
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0		0	0
Other Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	134	221	166	316
Included in income before taxes	(25)	(24)	(21)	(124)
Included in other comprehensive income	0	0	0	0
Purchases/additions	7	3	13	8
Settlements	0	0	0	0
Asset (liability) balance, end of period	116	200	116	200
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	(25)	(24)	(19)	(124)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	$ 0	(42)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0		0	$ 0
Trading Assets, Excluding Debt and Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period			1
Included in income before taxes			0
Included in other comprehensive income			0
Purchases/additions			0
Settlements			0
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period			0
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	$ 0		$ 0