Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic earnings per share:
Income from operations attributable to common shareholders	$ 318	$ 392	$ 501	$ 670
Net income available for common stock	$ 318	$ 392	$ 501	$ 670
Weighted average common shares outstanding (in shares)	375,000,000	326,000,000	367,000,000	326,000,000
Basic earnings per share - continuing operations (in dollars per share)	$ 0.85	$ 1.20	$ 1.37	$ 2.05
Diluted earnings per share:
Income from operations attributable to common shareholders	$ 318	$ 392	$ 501	$ 670
Net income available for common stock	318	392	501	670
Net income available to common shareholders and assumed conversions	$ 318	$ 392	$ 501	$ 670
Weighted average common shares outstanding (in shares)	375,000,000	326,000,000	367,000,000	326,000,000
Incremental shares from assumed conversions (in shares)	1,000,000	1,000,000	1,000,000	1,000,000
Adjusted weighted average shares - diluted (in shares)	376,000,000	327,000,000	368,000,000	327,000,000
Diluted earnings per share - continuing operations (in dollars per share)	$ 0.85	$ 1.20	$ 1.36	$ 2.05
Stock option awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock-based compensation awards excluded from the computation of diluted earnings per share (in shares)	9,187,178	7,426,319	8,587,661	7,435,580