Fair Value Measurement and Fair Value of Financial Instruments - Reconciliation of Assets and Liabilities on a Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset balance, end of period	$ 8
Securities Available for Sale
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset balance, beginning of period	1,331	$ 1,600
Total gains (losses) (realized/unrealized) included in income before taxes, assets	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	31	(9)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	57	126
Settlements, assets	(288)	(386)
Asset balance, end of period	1,131	1,331
Changes in unrealized gains (losses) included in income before taxes for assets still held at end of period, assets	0	0
Other Assets
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Asset balance, beginning of period	277	65
Total gains (losses) (realized/unrealized) included in income before taxes, assets	(88)	(8)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	396	220
Settlements, assets	0	0
Asset balance, end of period	316	277
Changes in unrealized gains (losses) included in income before taxes for assets still held at end of period, assets	(103)	(8)
Trading Liabilities
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liability balance, beginning of period	(13)
Total gains (losses) (realized/unrealized) included in income before taxes, assets, liability	(4)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	9
Liability balance, end of period		(13)
Changes in unrealized gains (losses) included in income before taxes for assets still held at end of period, liabilities	(4)
Other Liabilities
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liability balance, beginning of period	(118)	(119)
Total gains (losses) (realized/unrealized) included in income before taxes, assets, liability	(6)	1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	0	0
Liability balance, end of period	(124)	(118)
Changes in unrealized gains (losses) included in income before taxes for assets still held at end of period, liabilities	(6)	1
Fair Value, Measurements, Recurring
Reconciliation of assets measured using significant unobservable inputs
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	$ 264	$ 354
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Percentage of Assets Fair Value Disclosure	100.00%	100.00%
Percentage of Assets Fair Value Disclosure, Netting Adjustment	(1.00%)	(1.00%)
Percentage of Company Assets Fair Value Disclosure	17.00%	17.00%
Percentage of Company Assets Fair Value Disclosure, Netting Adjustment	0.00%	0.00%
Fair Value, Measurements, Recurring | Level 3
Reconciliation of assets measured using significant unobservable inputs
Other assets	$ 316	$ 277
Assets, Fair Value Disclosure	$ 1,455	$ 1,621
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Percentage of Assets Fair Value Disclosure	5.00%	6.00%
Percentage of Company Assets Fair Value Disclosure	1.00%	1.00%
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	$ 10	$ 9
Assets, Fair Value Disclosure	$ 153	$ 155
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Percentage of Assets Fair Value Disclosure	1.00%	0.00%
Percentage of Company Assets Fair Value Disclosure	0.00%	0.00%
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	$ 10	$ 32
Assets, Fair Value Disclosure	$ 27,150	$ 26,404
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Percentage of Assets Fair Value Disclosure	95.00%	95.00%
Percentage of Company Assets Fair Value Disclosure	16.00%	16.00%
Mortgage servicing rights [Domain] | Fair Value, Measurements, Recurring | Level 3
Reconciliation of assets measured using significant unobservable inputs
Other assets	$ 270	$ 159
Mortgage servicing rights [Domain] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	0	0
Mortgage servicing rights [Domain] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	0	0
loans held for sale [Domain] | Fair Value, Measurements, Recurring | Level 3
Reconciliation of assets measured using significant unobservable inputs
Other assets	42	117
loans held for sale [Domain] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	0	0
loans held for sale [Domain] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	0	0
Derivative Financial Instruments, Assets [Member] | Fair Value, Measurements, Recurring
Reconciliation of assets measured using significant unobservable inputs
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	8	19
Derivative Financial Instruments, Assets [Member] | Fair Value, Measurements, Recurring | Level 3
Reconciliation of assets measured using significant unobservable inputs
Other assets	4	1
Derivative Financial Instruments, Assets [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	0	0
Derivative Financial Instruments, Assets [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	10	32
Equity Securities, FV-NI [Member] | Fair Value, Measurements, Recurring | Level 3
Reconciliation of assets measured using significant unobservable inputs
Other assets	0	0
Equity Securities, FV-NI [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	10	9
Equity Securities, FV-NI [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 [Member]
Reconciliation of assets measured using significant unobservable inputs
Other assets	0	0
Other Asset Liability Management Securities [Member] | Fair Value, Measurements, Recurring
Reconciliation of assets measured using significant unobservable inputs
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	8	19
Fair Value
Reconciliation of assets measured using significant unobservable inputs
Other assets	54	48
Fair Value | Fair Value, Measurements, Recurring
Reconciliation of assets measured using significant unobservable inputs
Other assets	328	299
Assets, Fair Value Disclosure	28,494	27,826
Fair Value | Mortgage servicing rights [Domain] | Fair Value, Measurements, Recurring
Reconciliation of assets measured using significant unobservable inputs
Other assets	270	159
Fair Value | loans held for sale [Domain] | Fair Value, Measurements, Recurring
Reconciliation of assets measured using significant unobservable inputs
Other assets	42	117
Fair Value | Derivative Financial Instruments, Assets [Member] | Fair Value, Measurements, Recurring
Reconciliation of assets measured using significant unobservable inputs
Other assets	6	14
Fair Value | Equity Securities, FV-NI [Member] | Fair Value, Measurements, Recurring
Reconciliation of assets measured using significant unobservable inputs
Other assets	$ 10	$ 9