Stockholders' Equity and EPS - Reclassifications out of AOCI (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification adjustment for losses (gains) included in net income	[1]			$ 45,172	$ 20,341
Related tax (benefit) expense		$ (77,287)	$ (71,656)	(151,253)	(123,061)
Net income available to common stockholders		237,798	123,193	432,759	224,676
Reclassification out of Accumulated Other Comprehensive Income | Gains on investment securities, net
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification adjustment for losses (gains) included in net income		0	123	0	(485)
Related tax (benefit) expense		0	(50)	0	198
Net income available to common stockholders		$ 0	$ 73	$ 0	$ (287)

[1] During the first quarter of 2018 we adopted ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. This guidance was adopted on a retrospective basis and impacted the presentation between investing and operating activities related to distributions and net gains from our nonmarketable and other securities portfolio. See Note 1—“Basis of Presentation” of the “Notes to Interim Consolidated Financial Statements (unaudited)” under Part I, Item 1 of this report for additional details.