Partnership Capital Subject to Mandatory Redemption - Roll Forward of Outstanding Partnership Loans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Partners Capital Notes [Abstract]
Partnership loans outstanding at beginning of year	$ 218	$ 198
Partnership loans issued during the year	146	119
Repayment of Partnership loans during the year	(98)	(99)
Partnership loans outstanding at end of year	$ 266	$ 218