Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Basic earnings per share
Net income attributable to common shareholders	$ 259	$ 183
Net income available for common stock	$ 259	$ 183
Weighted average common shares outstanding (in shares)	379,000,000	363,000,000
Basic earnings per share (in dollars per share)	$ 0.68	$ 0.50
Diluted earnings per share
Net income attributable to common shareholders	$ 259	$ 183
Net income available for common stock	259	183
Net income available to common shareholders and assumed conversions	$ 259	$ 183
Weighted average common shares outstanding (in shares)	379,000,000	363,000,000
Incremental shares from assumed conversions (in shares)	1,000,000	1,000,000
Adjusted weighted average shares - diluted (in shares)	380,000,000	364,000,000
Diluted earnings per share (in dollars per share)	$ 0.68	$ 0.50
Antidilutive stock option awards excluded from earnings per share, number of shares	11,412,075	3,362,329