Stock Repurchase Plan Stock Repurchase Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock Repurchase Plan [Abstract]
Authorized common stock repurchase amount			$ 1,250.0
Common stock repurchased, shares	0	0	36,994,653
Common stock repurchased, purchase price			$ 994.8