Equity-Based Compensation - Stock Options (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Weighted Average Per Share Fair Value, beginning of year	$ 45.12
Granted, Weighted Average Per Share Fair Value	65.45
Exercised, Weighted Average Per Share Fair Value	42.19
Forfeited or expired, Weighted Average Per Share Fair Value	53.35
Outstanding, Weighted Average Per Share Fair Value, end of year	53.46	$ 45.12
Exercisable, weighted average per share exercise price	$ 41.56
Exercise of common stock options	$ 95	$ 63	$ 77
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of awards	10 years
Outstanding shares, beginning of year	5,643
Granted, shares	1,732
Exercised, shares	(2,331)
Forfeited or expired, shares	(159)
Outstanding shares, end of year	4,885	5,643
Exercisable shares, end of year	2,124
Weighted average remaining contractual term of stock options outstanding	6 years 6 months
Aggregate intrinsic value of stock options outstanding based on the market value of company's common stock	$ 160
Aggregate intrinsic value of stock options exercisable based on the market value of company's common stock	95
Exercise of common stock options	95	$ 63	77
Aggregate intrinsic value of stock options exercised	$ 71	$ 67	$ 37
First Anniversary [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting (as a percent)	25.00%
Second Anniversary [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting (as a percent)	25.00%
Third Anniversary [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting (as a percent)	50.00%