Shareholders' Equity - Common Stock (Details) - USD ($)	3 Months Ended							6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2021	Jun. 30, 2020	Jul. 31, 2021	Apr. 30, 2021	Jan. 31, 2021	Jun. 30, 2019
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase											$ 425,000,000	$ 475,000,000	$ 2,000,000,000.0
Subsequent Event | Forecast
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase										$ 3,000,000,000.0
2019 Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased	$ 425,000,000	$ 0	$ 0	$ 0	$ 500,000,000	$ 500,000,000	$ 500,000,000	$ 900,000,000	$ 500,000,000