Business Segments - Additional Information (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) segment	Sep. 30, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			1
Out of Period Adjustment [Member]
Segment Reporting Information [Line Items]
Group Reporting Basis Loan impairment charges (Provision for credit losses)			$ 16
Group Reporting Basis Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Cumulative impact of correction of an error			100
Group Reporting Basis Loan impairment charges (Provision for credit losses)	$ 14	$ (13)	$ 113	$ 36