Stockholders' Equity and EPS Reclassification of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification adjustment for (gains) losses included in net income									$ 89,445	[1]	$ 267,023		$ 419,408
Related tax expense (benefit)	$ (53,697)	$ (57,017)	$ (54,974)	$ (63,066)	$ (46,077)	$ (40,207)	$ (35,928)	$ (61,296)	(228,754)	[2]	(183,508)	[2]	(146,830)	[2]
Net income available to common stockholders	$ 87,512	$ 81,733	$ 86,143	$ 88,516	$ 57,990	$ 63,977	$ 50,953	$ 90,950	343,904	[1],[2]	263,870	[2]	214,517	[2]
Accumulated Net Unrealized Investment Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification adjustment for (gains) losses included in net income									(1,201)		18,598		(538)
Related tax expense (benefit)									481		(7,510)		218
Net income available to common stockholders									$ (720)		$ 11,088		$ (320)

[1] During the second quarter of 2015 we adopted new accounting guidance related to our consolidated variable interest entities (ASU 2015-02). Amounts prior to January 1, 2015 have not been revised for the adoption of this guidance. See Note 2— "Summary of Significant Accounting Policies” of the “Notes to the Consolidated Financial Statements” under Part II, Item 8 of this report for additional details.

[2] Prior period amounts have been revised to reflect the retrospective application of new accounting guidance adopted in the first quarter of 2015 related to our investments in qualified affordable housing projects (ASU 2014-01). See Note 2— "Summary of Significant Accounting Policies” of the “Notes to the Consolidated Financial Statements” under Part II, Item 8 of this report for additional details.