Consolidated Statements of Shareholders' Equity Parenthetical - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Issuance of shares under equity-based compensation plans - net, net of income tax benefit	$ 1	$ 1	$ 20