Stock Repurchases (Details) - USD ($) shares in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 16, 2018
Stockholders' Equity Note [Abstract]
Stock repurchase program, authorized amount	$ 2,500,000,000		$ 500,000,000
Stock repurchase program, remaining authorized amount	$ 346,000,000
Stock Repurchased During Period, Shares	0.4
Stock Repurchased During Period, Value	$ 100,000,000.0
Shares repurchased from employees who surrendered shares to satisfy minimum tax withholding obligations	0.1
Shares repurchased from employees who surrendered shares to satisfy minimum tax withholding obligations, value	$ 13,500,000	$ 18,100,000