Stock Repurchases (Details) - USD ($) shares in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 13, 2019
Stock Repurchased During Period, Shares	0.5	0.6	0.4
Stock Repurchased During Period, Value	$ 150,000,000.0	$ 150,000,000.0	$ 100,000,000.0
Authorized amount for share repurchase				$ 3,000,000,000			$ 500,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount				$ 546,000,000
Repurchased shares to satisfy minimum withholding obligations (in shares)				0.1	0.1
Repurchased shares to satisfy employee withholding tax obligations				$ 24,000,000.0	$ 26,900,000	$ 26,100,000