Segment Information - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Percent of maximum revenue from single customer on total revenues	10.00%
Hudson City [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Increase (decrease) in net interest income		$ 12
Increase (decrease) in income tax expense		5
Increase (decrease) in net income		7
Hudson City [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Increase (decrease) in net interest income		(12)
Increase (decrease) in income tax expense		(5)
Increase (decrease) in net income		$ (7)