Fair Value Measurements - Assets and Liabilities Measured at Recurring Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Assets:
Available-for-sale debt securities, fair value	$ 35,753	$ 32,830
Trading debt securities	322	287
Equity securities	485	452
Mortgage servicing rights	1,039		$ 959
Total assets	225		327
Commercial
Assets:
Loans held for sale measured at FV	18	7
Residential Mortgage Loans
Assets:
Loans measured at FV	192	179
Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	35,207	32,278
Trading debt securities	322	287
Equity securities	485	452
Residential mortgage loans held for sale	1,031	537
Loans measured at FV	192	179
Loans held for sale measured at FV	18	7
Mortgage servicing rights	1,039	938
Derivative assets	1,700	1,114
Total assets	39,994	35,792
Liabilities:
Derivative liabilities	1,202	874
Short positions	(153)	(138)
Total liabilities	1,355	1,012
Interest Rate Contract \| Fair value, recurring
Assets:
Derivative assets	1,290	655
Liabilities:
Derivative liabilities	655	329
Foreign Exchange Contract \| Fair value, recurring
Assets:
Derivative assets	135	152
Liabilities:
Derivative liabilities	135	142
Equity Contract \| Fair value, recurring
Liabilities:
Derivative liabilities	151	125
Commodity Contract \| Fair value, recurring
Assets:
Derivative assets	275	307
Liabilities:
Derivative liabilities	261	278
U.S. Treasury and federal agency
Assets:
Available-for-sale debt securities, fair value	75	97
U.S. Treasury and federal agency \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	75	97
Trading debt securities	15	16
Obligations of states and political subdivisions
Assets:
Available-for-sale debt securities, fair value	3	2
Obligations of states and political subdivisions \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	3	2
Trading debt securities	31	35
Agency mortgage-backed securities \| Residential mortgage backed securities
Assets:
Available-for-sale debt securities, fair value	14,802	16,247
Agency mortgage-backed securities \| Residential mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	14,802	16,247
Trading debt securities	77	68
Agency mortgage-backed securities \| Commercial mortgage backed securities
Assets:
Available-for-sale debt securities, fair value	14,820	10,650
Agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	14,820	10,650
Non-agency mortgage-backed securities \| Commercial mortgage backed securities
Assets:
Available-for-sale debt securities, fair value	3,380	3,267
Non-agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	3,380	3,267
Asset-backed securities and other debt securities
Assets:
Available-for-sale debt securities, fair value	2,127	2,015
Asset-backed securities and other debt securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	2,127	2,015
Trading debt securities	199	168
Fair Value, Inputs, Level 1
Assets:
Total assets	0		0
Fair Value, Inputs, Level 1 \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	75	97
Trading debt securities	2	0
Equity securities	476	452
Residential mortgage loans held for sale	0	0
Loans measured at FV	0	0
Loans held for sale measured at FV	0	0
Mortgage servicing rights	0	0
Derivative assets	65	93
Total assets	618	642
Liabilities:
Derivative liabilities	24	27
Short positions	(97)	(110)
Total liabilities	121	137
Fair Value, Inputs, Level 1 \| Interest Rate Contract \| Fair value, recurring
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	13	8
Fair Value, Inputs, Level 1 \| Foreign Exchange Contract \| Fair value, recurring
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 1 \| Equity Contract \| Fair value, recurring
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 1 \| Commodity Contract \| Fair value, recurring
Assets:
Derivative assets	65	93
Liabilities:
Derivative liabilities	11	19
Fair Value, Inputs, Level 1 \| U.S. Treasury and federal agency \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	75	97
Trading debt securities	2	0
Fair Value, Inputs, Level 1 \| Obligations of states and political subdivisions \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 1 \| Agency mortgage-backed securities \| Residential mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 1 \| Agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 1 \| Non-agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 1 \| Asset-backed securities and other debt securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 2
Assets:
Total assets	17		50
Fair Value, Inputs, Level 2 \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	35,132	32,181
Trading debt securities	320	287
Equity securities	9	0
Residential mortgage loans held for sale	1,031	537
Loans measured at FV	0	0
Loans held for sale measured at FV	18	7
Mortgage servicing rights	0	0
Derivative assets	1,621	1,014
Total assets	38,131	34,026
Liabilities:
Derivative liabilities	1,018	714
Short positions	(56)	(28)
Total liabilities	1,074	742
Fair Value, Inputs, Level 2 \| Interest Rate Contract \| Fair value, recurring
Assets:
Derivative assets	1,276	648
Liabilities:
Derivative liabilities	633	313
Fair Value, Inputs, Level 2 \| Foreign Exchange Contract \| Fair value, recurring
Assets:
Derivative assets	135	152
Liabilities:
Derivative liabilities	135	142
Fair Value, Inputs, Level 2 \| Equity Contract \| Fair value, recurring
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 2 \| Commodity Contract \| Fair value, recurring
Assets:
Derivative assets	210	214
Liabilities:
Derivative liabilities	250	259
Fair Value, Inputs, Level 2 \| U.S. Treasury and federal agency \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	13	16
Fair Value, Inputs, Level 2 \| Obligations of states and political subdivisions \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	3	2
Trading debt securities	31	35
Fair Value, Inputs, Level 2 \| Agency mortgage-backed securities \| Residential mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	14,802	16,247
Trading debt securities	77	68
Fair Value, Inputs, Level 2 \| Agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	14,820	10,650
Fair Value, Inputs, Level 2 \| Non-agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	3,380	3,267
Fair Value, Inputs, Level 2 \| Asset-backed securities and other debt securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	2,127	2,015
Trading debt securities	199	168
Fair Value, Inputs, Level 3
Assets:
Total assets	208		$ 277
Fair Value, Inputs, Level 3 \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Equity securities	0	0
Residential mortgage loans held for sale	0	0
Loans measured at FV	192	179
Loans held for sale measured at FV	0	0
Mortgage servicing rights	1,039	938
Derivative assets	14	7
Total assets	1,245	1,124
Liabilities:
Derivative liabilities	160	133
Short positions	0	0
Total liabilities	160	133
Fair Value, Inputs, Level 3 \| Interest Rate Contract \| Fair value, recurring
Assets:
Derivative assets	14	7
Liabilities:
Derivative liabilities	9	8
Fair Value, Inputs, Level 3 \| Foreign Exchange Contract \| Fair value, recurring
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 3 \| Equity Contract \| Fair value, recurring
Liabilities:
Derivative liabilities	151	125
Fair Value, Inputs, Level 3 \| Commodity Contract \| Fair value, recurring
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 3 \| U.S. Treasury and federal agency \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 3 \| Obligations of states and political subdivisions \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 3 \| Agency mortgage-backed securities \| Residential mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 3 \| Agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 3 \| Non-agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 3 \| Asset-backed securities and other debt securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Fair value of financial and nonfinancial obligations.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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The net of non investment assets and liabilities. This amount represents the difference between the aggregate value of the investments, including long and short positions, and net assets.

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Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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