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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, end of period	$ 2		$ 2
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Settlements		$ 0
Trading derivatives
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	(3)	(12)		$ (13)
Included in income before taxes	0	0		2
Included in other comprehensive income	0	0		0
Purchases/additions	0	0		0
Settlements	1	0		3
Asset (liability) balance, end of period	(2)	(12)	(2)	(12)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	0	0		(2)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0
Other Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	(124)	(119)	(124)	(118)
Included in income before taxes	(2)	6	(2)	7
Included in other comprehensive income	0	0	0	0
Purchases/additions	0	0	0	0
Settlements	14		14	0
Asset (liability) balance, end of period	(108)	(125)	(108)	(125)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	1	(6)	1	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0
Trading Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period			(8)
Included in income before taxes			(3)
Included in other comprehensive income			0
Purchases/additions			0
Settlements			3
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period			3
Trading derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	3	12		13
Included in income before taxes	0	0		2
Included in other comprehensive income	0	0		0
Purchases/additions	0	0		0
Settlements	(1)	0		(3)
Asset (liability) balance, end of period	2	12	2	12
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	0	0		2
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
Securities Available for Sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	1,123	1,268	1,131	1,331
Included in income before taxes	0	0	0	0
Included in other comprehensive income	4	9	1	20
Purchases/additions	29	2	30	4
Settlements	(31)	(191)	(37)	(267)
Asset (liability) balance, end of period	1,125	1,088	1,125	1,088
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
Other Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	221	386	316	277
Included in income before taxes	(24)	(45)	(124)	(76)
Included in other comprehensive income	0	0	0	0
Purchases/additions	3	178	8	318
Settlements	0	0	0	0
Asset (liability) balance, end of period	200	519	200	519
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	(24)	(45)	(124)	$ (76)
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
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			8
Included in income before taxes			(3)
Included in other comprehensive income			0
Purchases/additions			0
Settlements			(3)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period			$ (3)