Securities - Cumulative Credit Portion of Impairments on Debt Securities (Detail) $ in Millions	3 Months Ended
	Jun. 30, 2016 USD ($)
Investments, Debt and Equity Securities [Abstract]
Cumulative Impairments on Debt Securities, Beginning Balance	$ 4
Impairment recognized in earnings	0
Cumulative Impairments on Debt Securities, Ending Balance	$ 4