Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic (loss) earnings per share – continuing operations:
(Loss) income from continuing operations, net of tax									$ (457)	$ 565	$ 1,299
Participating securities dividends									0	0	0
(Loss) income from continuing operations available to common shareholders									$ (457)	$ 565	$ 1,299
Weighted average common shares outstanding (in shares)									326,000,000	326,000,000	326,000,000
Basic (loss) earnings per share – continuing operations (in dollars per share)	$ (4.49)	$ 1.57	$ 0.85	$ 0.67	$ (1.67)	$ 1.44	$ 0.85	$ 1.11	$ (1.40)	$ 1.73	$ 3.99
Diluted (loss) earnings per share – continuing operations:
(Loss) income from continuing operations attributable to common shareholders									$ (457)	$ 565	$ 1,299
Participating securities dividends									0	0	0
(Loss) income from continuing operations available to common shareholders									(457)	565	1,299
Income impact of assumed conversions									0	0	1
(Loss) income from continuing operations available to common shareholders and assumed conversions									$ (457)	$ 565	$ 1,300
Weighted average common shares outstanding (in shares)									326,000,000	326,000,000	326,000,000
Incremental shares from assumed conversions (in shares)									0	2,000,000	4,000,000
Adjusted weighted average shares - diluted (in shares)									326,000,000	328,000,000	330,000,000
Diluted (loss) earnings per share – continuing operations (in dollars per share)	$ (4.49)	$ 1.57	$ 0.84	$ 0.67	$ (1.66)	$ 1.43	$ 0.85	$ 1.10	$ (1.40)	$ 1.72	$ 3.94
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									8,852,706	1,334,451	167,795