Investment Securities - Investment Securities Held to Maturity (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 28,636	$ 26,701
Unrealized Losses Recorded in AOCI	(916)	(989)
Carrying Value	27,720	25,712
Gross Unrealized Gains	825	683
Gross Unrealized Losses	(122)	(199)
Fair Value	28,423	26,196
U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	199	199
Unrealized Losses Recorded in AOCI	0	0
Carrying Value	199	199
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	199	199
Agency \| RMBS
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	24,741	23,022
Unrealized Losses Recorded in AOCI	(831)	(897)
Carrying Value	23,910	22,125
Gross Unrealized Gains	724	606
Gross Unrealized Losses	(97)	(158)
Fair Value	24,537	22,573
Agency \| CMBS
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,696	3,480
Unrealized Losses Recorded in AOCI	(85)	(92)
Carrying Value	3,611	3,388
Gross Unrealized Gains	101	77
Gross Unrealized Losses	(25)	(41)
Fair Value	$ 3,687	$ 3,424

Unrealized losses recorded in AOCI on held to maturity securities.

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- Definition

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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