Computation of Earnings per Common Share - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 140	$ 107	$ 421	$ 296
Less: Dividends paid on and earnings allocated to participating securities	(2)	(1)	(5)	(4)
Earnings applicable to common stock	$ 138	$ 106	$ 416	$ 292
Weighted average common shares outstanding	464,047,337	461,780,959	463,813,827	462,898,726
Basic earnings per common share	$ 0.30	$ 0.23	$ 0.90	$ 0.63
Earnings applicable to common stock	$ 138	$ 106	$ 416	$ 292
Potential dilutive common shares	834,612	864,855	744,292	614,082
Total shares for diluted earnings per common share computation	464,881,949	462,645,814	464,558,119	463,512,808
Diluted earnings per common share and common share equivalents	$ 0.30	$ 0.23	$ 0.90	$ 0.63