Equity-Based Compensation Information Related to Stock Options (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Pretax expense for stock options	$ 14	$ 12	$ 12
After-tax expense for stock options	9	8	8
Proceeds from stock options exercised	74	52	54
Income tax benefit related to stock options exercised
Tax benefit classified in operating activities in the Consolidated Statements of Cash Flows	5	4	4
Excess tax benefit classified in financing activities in the Consolidated Statements of Cash Flows	1	1	15
Intrinsic value of stock options exercised	42	44	55
Total fair value of stock options vested	$ 14	$ 12	$ 12
Stock options exercised, in millions of options	1.9	1.4	1.5
Non-vested stock option compensation expense not yet recognized	$ 11
Non-vested stock options weighted-average period for total compensation expense to be recognized ( in years)	1 year 10 months 24 days