Partnership Capital Subject to Mandatory Redemption - Roll Forward of Outstanding Partnership Loans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Other Liabilities Disclosure [Abstract]
Partnership loans outstanding at beginning of year	$ 198	$ 215
Partnership loans issued during the year	119	86
Repayment of Partnership loans during the year	(99)	(103)
Partnership loans outstanding at end of year	$ 218	$ 198