Condensed Consolidated Statements of Shareholder's Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Surplus	Accumulated Deficit	Accumulated Other Comprehensive Loss	Non-Controlling Interests
Balance, beginning of period at Dec. 31, 2016	$ 12,750,707	$ 229,475	$ 2,230	$ 14,985,673	$ (2,327,440)	$ (168,252)	$ 29,021
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	120,823				120,380		443
Other comprehensive income, net of tax	17,471					17,471
Preferred stock dividends	(3,548)			(3,548)
Capital contribution	46						46
Balance, end of period at Mar. 31, 2017	12,885,499	229,475	2,230	14,982,125	(2,207,060)	(150,781)	29,510
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect from adoption of ASU 2016-01					13	(13)
Balance, as adjusted	13,013,310	229,475	2,230	14,818,608	(1,868,646)	(197,418)	29,061
Balance, beginning of period at Dec. 31, 2017	13,013,310	229,475	2,230	14,818,608	(1,868,659)	(197,405)	29,061
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	208,690				208,229		461
Other comprehensive income, net of tax	(74,013)					(74,013)
Preferred stock dividends	(3,864)			(3,864)
Capital contribution	16						16
Balance, end of period at Mar. 31, 2018	$ 13,144,139	$ 229,475	$ 2,230	$ 14,814,744	$ (1,660,417)	$ (271,431)	$ 29,538