Cash Flow Information - Schedule of Supplemental Cash Flow Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash paid for interest	$ 125	$ 90	$ 75
Cash paid for taxes	10	10	12
Non-cash activities:
Issuance of general partnership interests through partnership loans in current year	170	142	146
Repayment of partnership loans through distributions from partnership capital in current year	135	$ 111	$ 98
Declared distributions for retired partnership capital in current year but paid after year end	$ 97