Equity-Based Compensation - PSUs (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Feb. 28, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years	3 years
Vested shares issued, percentage of the established target			200.00%
Range of potential payout (as a percent)		100.00%
Unvested, Units, beginning of year		1,164
Granted, Units		364
Vested, Units	(853,000)	(427)
Forfeited, Units		(24)
Unvested, Units, end of year		1,077	1,164
Unvested, Weighted Average Per Share Fair Value, beginning of year		$ 90.17
Granted, Weighted Average Per Share Fair Value		116.26
Vested, Weighted Average Per Share Fair Value		93.03
Forfeited, Weighted Average Per Share Fair Value		98.33
Unvested, Weighted Average Per Share Fair Value, end of year		$ 99.66	$ 90.17
Shares issued under the plan	532,000
Total fair market value of vested awards		$ 84	$ 78	$ 80
Deferred Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested deferred units outstanding		225,000
Minimum [Member] | Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of potential payout (as a percent)		0.00%
Maximum [Member] | Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of potential payout (as a percent)		200.00%