Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Preferred Stock [Member]	Common Stock, par value $0.01 per share	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Balance at beginning of period at Dec. 31, 2017	$ 4,409	$ 107	$ 3	$ 4,033	$ 368	$ (83)	$ (19)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	139				172	(33)
Dividends declared:
Preferred stock	(4)				(4)
Common stock	(79)				(79)
Issuance of common stock	3			5			(2)
Restricted stock compensation	5			5
Balance at end of period at Jun. 30, 2018	4,473	107	3	4,043	457	(116)	(21)
Balance at beginning of period at Mar. 31, 2018	4,433	107	3	4,037	414	(109)	(19)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	78				85	(7)
Dividends declared:
Preferred stock	(2)				(2)
Common stock	(40)				(40)
Issuance of common stock	1			3			(2)
Restricted stock compensation	3			3
Balance at end of period at Jun. 30, 2018	4,473	107	3	4,043	457	(116)	(21)
Balance at beginning of period at Dec. 31, 2018	4,608	107	3	4,049	576	(106)	(21)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	223				189	34
Dividends declared:
Preferred stock	(4)				(4)
Common stock	(78)				(78)
Issuance of common stock	(2)			2			(4)
Restricted stock compensation	6			6
Balance at end of period at Jun. 30, 2019	4,753	107	3	4,057	683	(72)	(25)
Balance at beginning of period at Mar. 31, 2019	4,680	107	3	4,052	629	(88)	(23)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	111				95	16
Dividends declared:
Preferred stock	(2)				(2)
Common stock	(39)				(39)
Issuance of common stock	(1)			1			(2)
Restricted stock compensation	4			4
Balance at end of period at Jun. 30, 2019	$ 4,753	$ 107	$ 3	$ 4,057	$ 683	$ (72)	$ (25)