Realized Gains and Losses Recognized in Income from Available-for-Sale Securities (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Interest-Only Mortgage-Backed Securities
Investment Holdings [Line Items]
Net gains/losses on interest-only mortgage-backed securities	$ 11	$ (8)	$ 2	$ (7)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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