Share-based Compensation - Share-based Compensation Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense before income taxes	$ 73	$ 97	$ 83
Income tax benefit on share-based compensation expense	28	36	31
Restricted Stock
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense before income taxes	45	67	62
Stock Options
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense before income taxes	7	5	2
Performance Share Units
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense before income taxes	$ 21	$ 25	$ 19