Stockholders' Equity (Narrative) (Details) - USD ($) shares in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Stockholders' Equity Note [Abstract]
Payments of dividends (in dollars per share)	$ 120,200,000	$ 0
Stock repurchase program, authorized amount	$ 500,000,000
Shares repurchased (in shares)	7.7
Shares repurchased, value	$ 242,000,000