Equity-Based Compensation - Assumptions (Detail) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) item $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred income tax benefits include in income tax expense	$ 32	$ 37
Employee Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense recognized		92	$ 81	$ 64
Deferred income tax benefits include in income tax expense		36	$ 32	$ 26
Currently unrecognized compensation expense		$ 62
Weighted average period unrecognized compensation expenses expected to be recognized		1 year 4 months 24 days
Non-Employee Director Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of installments | item		2
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of stock options granted | $ / shares		$ 11.71	$ 6.31	$ 5.56
Expected option life		3 years 6 months	4 years 8 months 12 days	4 years 4 months 24 days
Expected volatility		15.30%	18.40%	16.70%
Expected dividend yield		2.30%	2.90%	2.80%
Risk-free interest rate		1.70%	1.30%	1.40%