Consolidated Statement of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Series A Preferred Stock [Member] Preferred Stock [Member]	Series B Preferred Stock [Member] Preferred Stock [Member]	Series C Preferred Stock [Member] Preferred Stock [Member]
Balance, value at Dec. 31, 2015	$ 7,971.0	$ 3.0	$ 10,048.0	$ (2,350.0)	$ (66.0)	$ 167.0	$ 169.0	$ 0.0
Balance, Common Stock, shares at Dec. 31, 2015		337.5
Net income (loss)	623.0			623.0
Other comprehensive income (loss):
Unrealized Gains and (Losses), Net	(370.0)				(370.0)
Amounts reclassified from accumulated OCI	39.0				(39.0)
Proceeds from Issuance of Preferred Stock and Preference Stock	0.0
Issuance costs of redeemed preferred stock	0.0
Repurchase of common stock	(116.0)	$ 0.0	116.0
Payments for Repurchase of Common Stock	$ 116.0
Repurchase of common stock shares	(6.5)	(6.5)
Preferred dividends declared	$ (28.0)			(28.0)
Common dividends declared	(763.0)			(763.0)
Balance, value at Dec. 31, 2016	7,356.0	$ 3.0	9,932.0	(2,518.0)	(397.0)	167.0	169.0	0.0
Balance, Common Stock, shares at Dec. 31, 2016		331.0
Net income (loss)	771.0			771.0
Other comprehensive income (loss):
Unrealized Gains and (Losses), Net	52.0				52.0
Amounts reclassified from accumulated OCI	0.0
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options	4.0		4.0
Proceeds from Issuance of Preferred Stock and Preference Stock	$ 315.0
Stock Redeemed or Called During Period, Shares	(167.0)
Preferred Stock, Redemption Amount	$ (173.0)
Issuance costs of redeemed preferred stock	(6.0)
Stock Issued During Period, Shares, New Issues		60.3
Stock Issued During Period, Value, New Issues	1,238.0	$ 1.0	1,237.0
Payments for Repurchase of Common Stock	0.0
Preferred dividends declared	(32.0)			(32.0)
Common dividends declared	(777.0)			(777.0)
Balance, value at Dec. 31, 2017	$ 8,754.0	$ 4.0	11,173.0	(2,562.0)	(345.0)	0.0	169.0	315.0
Balance, Common Stock, shares at Dec. 31, 2017	391.3	391.3
Net income (loss)	$ 129.0			129.0
Other comprehensive income (loss):
Unrealized Gains and (Losses), Net	(598.0)				(598.0)
Amounts reclassified from accumulated OCI	0.0
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options	10.0		10.0
Proceeds from Issuance of Preferred Stock and Preference Stock	0.0
Issuance costs of redeemed preferred stock	0.0
Stock Issued During Period, Shares, New Issues		145.0
Stock Issued During Period, Value, New Issues	2,611.0	$ 1.0	2,610.0
Payments for Repurchase of Common Stock	0.0
Preferred dividends declared	(36.0)			(36.0)
Common dividends declared	(964.0)			(964.0)
Balance, value at Dec. 31, 2018	$ 9,906.0	$ 5.0	$ 13,793.0	$ (3,433.0)	$ (943.0)	$ 0.0	$ 169.0	$ 315.0
Balance, Common Stock, shares at Dec. 31, 2018	536.3	536.3