Fair Value Measurements - Assets and Liabilities Measured at Recurring Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Assets:
Available-for-sale debt securities, fair value	$ 37,178	$ 32,830
Trading debt securities	297	287
Equity securities	459	452
Mortgage servicing rights	910		$ 1,010
Total assets	193		314
Commercial
Assets:
Loans held for sale measured at FV	1	7
Residential Mortgage Loans
Assets:
Loans measured at FV	184	179
Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	36,603	32,278
Trading debt securities	297	287
Equity securities	459	452
Residential mortgage loans held for sale	1,136	537
Loans measured at FV	184	179
Loans held for sale measured at FV	1	7
Mortgage servicing rights	910	938
Derivative assets	2,097	1,114
Total assets	41,687	35,792
Liabilities:
Derivative liabilities	911	874
Short positions	(112)	(138)
Total liabilities	1,023	1,012
Interest Rate Contract \| Fair value, recurring
Assets:
Derivative assets	1,547	655
Liabilities:
Derivative liabilities	261	329
Foreign Exchange Contract \| Fair value, recurring
Assets:
Derivative assets	182	152
Liabilities:
Derivative liabilities	151	142
Equity Contract \| Fair value, recurring
Liabilities:
Derivative liabilities	146	125
Commodity Contract \| Fair value, recurring
Assets:
Derivative assets	368	307
Liabilities:
Derivative liabilities	353	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	3	16
Obligations of states and political subdivisions
Assets:
Available-for-sale debt securities, fair value	2	2
Obligations of states and political subdivisions \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	2	2
Trading debt securities	29	35
Agency mortgage-backed securities \| Residential mortgage backed securities
Assets:
Available-for-sale debt securities, fair value	15,694	16,247
Agency mortgage-backed securities \| Residential mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	15,694	16,247
Trading debt securities	69	68
Agency mortgage-backed securities \| Commercial mortgage backed securities
Assets:
Available-for-sale debt securities, fair value	15,276	10,650
Agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	15,276	10,650
Non-agency mortgage-backed securities \| Commercial mortgage backed securities
Assets:
Available-for-sale debt securities, fair value	3,400	3,267
Non-agency mortgage-backed securities \| Commercial mortgage backed securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	3,400	3,267
Asset-backed securities and other debt securities
Assets:
Available-for-sale debt securities, fair value	2,156	2,015
Asset-backed securities and other debt securities \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	2,156	2,015
Trading debt securities	196	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	449	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	92	93
Total assets	618	642
Liabilities:
Derivative liabilities	14	27
Short positions	(68)	(110)
Total liabilities	82	137
Fair Value, Inputs, Level 1 \| Interest Rate Contract \| Fair value, recurring
Assets:
Derivative assets	3	0
Liabilities:
Derivative liabilities	5	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	89	93
Liabilities:
Derivative liabilities	9	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	6		69
Fair Value, Inputs, Level 2 \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	36,528	32,181
Trading debt securities	295	287
Equity securities	10	0
Residential mortgage loans held for sale	1,136	537
Loans measured at FV	0	0
Loans held for sale measured at FV	1	7
Mortgage servicing rights	0	0
Derivative assets	1,981	1,014
Total assets	39,951	34,026
Liabilities:
Derivative liabilities	742	714
Short positions	(44)	(28)
Total liabilities	786	742
Fair Value, Inputs, Level 2 \| Interest Rate Contract \| Fair value, recurring
Assets:
Derivative assets	1,520	648
Liabilities:
Derivative liabilities	247	313
Fair Value, Inputs, Level 2 \| Foreign Exchange Contract \| Fair value, recurring
Assets:
Derivative assets	182	152
Liabilities:
Derivative liabilities	151	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	279	214
Liabilities:
Derivative liabilities	344	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	1	16
Fair Value, Inputs, Level 2 \| Obligations of states and political subdivisions \| Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	2	2
Trading debt securities	29	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	15,694	16,247
Trading debt securities	69	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	15,276	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	3,400	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	2,156	2,015
Trading debt securities	196	168
Fair Value, Inputs, Level 3
Assets:
Total assets	187		$ 245
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	184	179
Loans held for sale measured at FV	0	0
Mortgage servicing rights	910	938
Derivative assets	24	7
Total assets	1,118	1,124
Liabilities:
Derivative liabilities	155	133
Short positions	0	0
Total liabilities	155	133
Fair Value, Inputs, Level 3 \| Interest Rate Contract \| Fair value, recurring
Assets:
Derivative assets	24	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	146	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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