Stock Repurchases (Details) - USD ($) shares in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 13, 2019
Stock Repurchased During Period, Shares	0.4
Stock Repurchased During Period, Value	$ 100,000,000.0
Repurchased shares to satisfy minimum withholding obligations (in shares)		0.1	0.1	0.1
Repurchased shares to satisfy employee withholding tax obligations		$ 17,900,000	$ 24,000,000.0	$ 26,900,000
Authorized amount for share repurchase		3,000,000,000			$ 500,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 446,000,000
Repurchased shares to satisfy minimum withholding obligations (in shares)		0.1	0.1	0.1
Repurchased shares to satisfy employee withholding tax obligations		$ 17,900,000	$ 24,000,000.0	$ 26,900,000