Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic earnings (loss) per share – continuing operations:
Income (loss) from continuing operations, net of tax									$ 1,284	$ (457)	$ 565
Participating securities dividends									$ 0	0	0
Income (loss) from continuing operations available to common shareholders										$ (457)	$ 565
Weighted average common shares outstanding (in shares)									340,000,000	326,000,000	326,000,000
Basic earnings (loss) per share – continuing operations (in dollars per share)	$ 0.40	$ 1.36	$ 1.20	$ 0.85	$ (4.49)	$ 1.57	$ 0.85	$ 0.67	$ 3.78	$ (1.40)	$ 1.73
Diluted earnings (loss) per share – continuing operations:
Income (loss) from continuing operations attributable to common shareholders									$ 1,284	$ (457)	$ 565
Participating securities dividends									0	0	0
Income (loss) from continuing operations available to common shareholders										(457)	565
Income impact of assumed conversions									0	0	0
Income (loss) from continuing operations available to common shareholders and assumed conversions									$ 1,284	$ (457)	$ 565
Weighted average common shares outstanding (in shares)									340,000,000	326,000,000	326,000,000
Incremental shares from assumed conversions (in shares)									1,000,000	0	2,000,000
Adjusted weighted average shares – diluted (in shares)									341,000,000	326,000,000	328,000,000
Diluted (loss) earnings per share – continuing operations (in dollars per share)	$ 0.40	$ 1.35	$ 1.20	$ 0.85	$ (4.49)	$ 1.57	$ 0.84	$ 0.67	$ 3.77	$ (1.40)	$ 1.72
Stock Compensation Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive stock option awards excluded from earnings per share, number of shares									4,511,802	8,852,706	1,334,451