Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Parenthetical) (Detail) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Nonrecurring [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Transfer of commercial and consumer loans from held-to-maturity to held-for-sale, current fair value	$ 22	$ 7	$ 62