Supplemental Information about Changes to Accumulated Other Comprehensive Income - Summary of Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2016		Sep. 30, 2015		Sep. 30, 2016		Sep. 30, 2015
Unrealized investment gains (losses) on available for sale assets:
Realized (gains) losses	$ (3,482)	[1]	$ (5,140)	[2]	$ (7,780)	[1]	$ (7,872)	[2]
Amortization of (discount) premium	(202,720)	[1]	(193,213)	[2]	(601,415)	[1]	(579,632)	[2]
Total before tax	(201,461)	[1]	(199,009)	[2]	(596,253)	[1]	(590,209)	[2]
Tax	59,551	[1]	65,151	[2]	181,475	[1]	193,046	[2]
Net income	(151,869)	[1]	(145,386)	[2]	(414,331)	[1]	(394,144)	[2]
Pension adjustments:
Total reclassifications (after tax)	(1,229)		(2,252)		(2,373)		(678)
Unrealized Investment Gains (Losses) on Available for Sale Assets [Member]
Pension adjustments:
Total reclassifications (after tax)	(2,886)		(4,621)		(7,348)		(7,786)
Amortization of Prior Service Cost [Member]
Pension adjustments:
Pension adjustments reclassified out of accumulated other comprehensive income	120		81		360		244
Amortization of Actuarial Gain (Loss) [Member]
Pension adjustments:
Pension adjustments reclassified out of accumulated other comprehensive income	2,431		3,563		7,294		10,691
Pension Adjustments [Member]
Pension adjustments:
Pension adjustments reclassified out of accumulated other comprehensive income	2,551		3,644		7,654		10,935
Tax	(894)		(1,275)		(2,679)		(3,827)
Total reclassifications (after tax)	1,657		2,369		4,975		7,108
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Investment Gains (Losses) on Available for Sale Assets [Member]
Unrealized investment gains (losses) on available for sale assets:
Realized (gains) losses	(3,513)		(5,540)		(7,809)		(7,138)
Amortization of (discount) premium	(927)		(1,569)		(3,495)		(4,840)
Total before tax	(4,440)		(7,109)		(11,304)		(11,978)
Tax	1,554		2,488		3,956		4,192
Net income	$ (2,886)		$ (4,621)		$ (7,348)		$ (7,786)

[1] Due to the adoption of ASU 2016-09, certain balances related to excess tax benefits from stock compensation were adjusted prospectively as described in Note 2—New Accounting Standards.

[2] Certain prior year balances were adjusted to give effect to discontinued operations as described in Note 5—Discontinued Operations.