Stockholders' Equity - Share Repurchase Program (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Jun. 30, 2021	Apr. 19, 2021	Jul. 25, 2017
Equity, Class of Treasury Stock [Line Items]
Stock repurchased during period, value	$ 141,000,000	$ 115,000,000
Common Stock | Share Repurchase Program 2017
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 2,000,000,000
Stock repurchased during period (in shares)			981,676
Stock repurchased during period, value			$ 200,000,000
Stock repurchase program, remaining authorized repurchase amount			$ 2,300,000,000
Common Stock | Share Repurchase Program 2021
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount				$ 2,000,000,000