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
	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, end of period	$ 3
Trading derivatives
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period		$ (13)
Included in income before taxes		2
Included in other comprehensive income		0
Purchases/additions		0
Settlements		3
Asset (liability) balance, end of period	(3)	(12)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period		(2)
Other Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	(124)	(118)
Included in income before taxes	0	1
Included in other comprehensive income	0	0
Purchases/additions	0	0
Settlements	0	0
Asset (liability) balance, end of period	(124)	(119)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	0	(1)
Trading Liabilities [Member]
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	2
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		13
Included in income before taxes		2
Included in other comprehensive income		0
Purchases/additions		0
Settlements		(3)
Asset (liability) balance, end of period		12
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period		2
Securities Available for Sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	1,131	1,331
Included in income before taxes	0	0
Included in other comprehensive income	(3)	11
Purchases/additions	1	2
Settlements	(6)	(76)
Asset (liability) balance, end of period	1,123	1,268
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	0	0
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset (liability) balance, beginning of period	316	277
Included in income before taxes	(100)	(31)
Included in other comprehensive income	0	0
Purchases/additions	5	140
Settlements	0	0
Asset (liability) balance, end of period	221	386
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	(100)	$ (31)
Trading Assets, Excluding Debt and Equity Securities [Member]
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	(2)
Changes in unrealized gains (losses) included in income before taxes for assets and liabilities still held at end of period	$ (3)