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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Net income for common stock	$ 538	$ 493	$ 1,122	$ 1,058
Weighted average common shares outstanding – basic (shares)	353.4	334.5	346.8	334.1
Add: Incremental shares attributable to effect of potentially dilutive securities (shares)	0.7	0.9	0.7	0.9
Adjusted weighted average common shares outstanding – diluted (shares)	354.1	335.4	347.5	335.0
Net income per common share - basic (dollars per share)	$ 1.52	$ 1.47	$ 3.23	$ 3.17
Net income per common share - diluted (dollars per share)	$ 1.52	$ 1.47	$ 3.23	$ 3.16