Investment Securities - Investment Securities Held to Maturity (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 37,022	$ 29,823
Unrealized Losses Recorded in AOCI	(251)	(839)
Carrying Value	36,771	28,984
Gross Unrealized Gains	314	635
Gross Unrealized Losses	(466)	(182)
Fair Value	36,619	29,437
U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		200
Unrealized Losses Recorded in AOCI		0
Carrying Value		200
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		200
RMBS, Agency
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	33,299	25,741
Unrealized Losses Recorded in AOCI	(238)	(761)
Carrying Value	33,061	24,980
Gross Unrealized Gains	293	565
Gross Unrealized Losses	(377)	(150)
Fair Value	32,977	25,395
CMBS, Agency
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,723	3,882
Unrealized Losses Recorded in AOCI	(13)	(78)
Carrying Value	3,710	3,804
Gross Unrealized Gains	21	70
Gross Unrealized Losses	(89)	(32)
Fair Value	$ 3,642	$ 3,842

Debt securities, Held-to-maturities, Amortized cost excluding AOCI transfer mark

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Unrealized losses recorded in AOCI on held to maturity securities.

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

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-Publisher FASB
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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 accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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

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