Segment Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2015
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Decrease in revenues		$ 6	$ 12
Decrease in net income		3	5
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Increase in revenues		6	12
Increase in net income		$ 3	$ 5
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Increase in revenues	$ 25
Increase in net income	15
All Other [Member]
Segment Reporting Information [Line Items]
Decrease in revenues	25
Decrease in net income	$ 15