Investment Securities (Investment Securities) (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Investment Holdings
Available-for-sale debt securities, fair value	$ 38,645	$ 36,028
Available-for-sale debt securities, unrealized losses	(110)	(43)
Available-for-sale debt securities, unrealized gains	2,327	1,105
Available-for-sale debt securities, Amortized Cost	36,428	34,966
Held-to-maturity securities, fair value	17	17
Held-to-maturity, unrealized losses	0	0
Held-to-maturity, unrealized gains	0	0
Held-to-maturity securities, amortized cost	17	17
Trading debt securities, fair value	433	297
Equity securities, fair value	459	564
U.S. Treasury and federal agencies
Investment Holdings
Available-for-sale debt securities, fair value	78	75
Available-for-sale debt securities, unrealized losses	0	0
Available-for-sale debt securities, unrealized gains	4	1
Available-for-sale debt securities, Amortized Cost	74	74
Obligations of states and political subdivisions
Investment Holdings
Available-for-sale debt securities, fair value	17	18
Available-for-sale debt securities, unrealized losses	0	0
Available-for-sale debt securities, unrealized gains	0	0
Available-for-sale debt securities, Amortized Cost	17	18
Held-to-maturity securities, fair value	15	15
Held-to-maturity, unrealized losses	0	0
Held-to-maturity, unrealized gains	0	0
Held-to-maturity securities, amortized cost	15	15
Asset-backed securities and other debt securities
Investment Holdings
Available-for-sale debt securities, fair value	2,677	2,206
Available-for-sale debt securities, unrealized losses	(88)	(12)
Available-for-sale debt securities, unrealized gains	18	29
Available-for-sale debt securities, Amortized Cost	2,747	2,189
Held-to-maturity securities, fair value	2	2
Held-to-maturity, unrealized losses	0	0
Held-to-maturity, unrealized gains	0	0
Held-to-maturity securities, amortized cost	2	2
Other securities
Investment Holdings
Available-for-sale debt securities, fair value	616	556
Available-for-sale debt securities, unrealized losses	0	0
Available-for-sale debt securities, unrealized gains	0	0
Available-for-sale debt securities, Amortized Cost	616	556
Residential mortgage backed securities \| Agency mortgage-backed securities
Investment Holdings
Available-for-sale debt securities, fair value	14,144	14,115
Available-for-sale debt securities, unrealized losses	(16)	(19)
Available-for-sale debt securities, unrealized gains	810	388
Available-for-sale debt securities, Amortized Cost	13,350	13,746
Commercial mortgage-backed securities \| Agency mortgage-backed securities
Investment Holdings
Available-for-sale debt securities, fair value	17,798	15,693
Available-for-sale debt securities, unrealized losses	(5)	(12)
Available-for-sale debt securities, unrealized gains	1,408	564
Available-for-sale debt securities, Amortized Cost	16,395	15,141
Commercial mortgage-backed securities \| Non-agency mortgage-backed securities
Investment Holdings
Available-for-sale debt securities, fair value	3,315	3,365
Available-for-sale debt securities, unrealized losses	(1)	0
Available-for-sale debt securities, unrealized gains	87	123
Available-for-sale debt securities, Amortized Cost	$ 3,229	$ 3,242

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

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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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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