Shareholders' Equity - Common Stock (Details) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2019	Jun. 30, 2018
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased					$ 1,600,000,000
2019 Program
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase			$ 2,000,000,000.0
Common stock repurchased	$ 500,000,000	$ 500,000,000			1,000,000,000
2018 Program
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase						$ 1,200,000,000
Common stock repurchased			$ 300,000,000	$ 300,000,000	$ 600,000,000