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Shareholder's Equity (Details) - USD ($) $ in Millions	3 Months Ended
Shareholder's Equity (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at period start	$ 3,222
Net income (loss)	(308)	$ (50)
Other comprehensive income (loss), net	22	13
Comprehensive Income (Loss), Net	(286)	(37)
Balance at period end	2,927
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at period start	2	2
Cash dividends paid - preferred stock	0	0
Stock option and incentive plans, net	0	0
Net income (loss)	0	0
Other comprehensive income (loss), net	0	0
Comprehensive Income (Loss), Net	0	0
Balance at period end	2	2
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at period start	3,878	3,850
Cash dividends paid - preferred stock	0	0
Stock option and incentive plans, net	(1)	3
Net income (loss)	0	0
Other comprehensive income (loss), net	0	0
Comprehensive Income (Loss), Net	0	0
Balance at period end	3,879	3,853
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at period start	(233)	171
Cash dividends paid - preferred stock	(2)	(2)
Stock option and incentive plans, net	0	0
Net income (loss)	(308)	(50)
Other comprehensive income (loss), net	0	0
Comprehensive Income (Loss), Net	(308)	(50)
Balance at period end	(551)	136
AOCL Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at period start	(425)	(494)
Cash dividends paid - preferred stock	0	0
Stock option and incentive plans, net	0	0
Net income (loss)	0	0
Other comprehensive income (loss), net	22	13
Comprehensive Income (Loss), Net	22	13
Balance at period end	(403)	(481)
Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at period start	3,222	3,529
Cash dividends paid - preferred stock	(2)	(2)
Stock option and incentive plans, net	(1)	3
Net income (loss)	(308)	(50)
Other comprehensive income (loss), net	22	13
Comprehensive Income (Loss), Net	(286)	(37)
Balance at period end	$ 2,927	$ 3,510
Accounting Standards Update 2014-09 [Member] \| Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard				$ 0
Accounting Standards Update 2014-09 [Member] \| Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard				0
Accounting Standards Update 2014-09 [Member] \| Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard				17
Accounting Standards Update 2014-09 [Member] \| AOCL Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard				0
Accounting Standards Update 2014-09 [Member] \| Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard				$ 17
Accounting Standards Update 2014-09 \| Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard			$ 0
Accounting Standards Update 2014-09 \| Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard			0
Accounting Standards Update 2014-09 \| Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard			(8)
Accounting Standards Update 2014-09 \| AOCL Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard			0
Accounting Standards Update 2014-09 \| Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative impact of adopting the new lease standard			$ (8)