Summary of Significant Accounting Policies and Other Matters - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounting Policies [Abstract]
Net income for common stock	$ 419	$ 375
Weighted average common shares outstanding – basic (shares)	342.2	333.6
Add: Incremental shares attributable to effect of potentially dilutive securities (shares)	0.8	1.0
Adjusted weighted average common shares outstanding – diluted (shares)	343.0	334.6
Net income per common share - basic (dollars per share)	$ 1.23	$ 1.13
Net income per common share - diluted (dollars per share)	$ 1.22	$ 1.12