Shareholders' Equity - Common Stock (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2019
2018 Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased	$ 300,000,000	$ 300,000,000	$ 600,000,000
2019 Program
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase	$ 2,000,000,000.0		$ 2,000,000,000.0