Investment Securities - Summary of Remaining Contractual Principal Maturities and Fully Taxable Equivalent Yields on Debt Securities Classified as Held to Maturity (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Federal statutory tax rate	35.00%
Amortized Cost	$ 5,463,920	$ 0
Weighted- Average Yield	1.41%
One Year or Less - Amortized Cost	3,351
One Year or Less - Weighted- Average Yield	1.36%
One Year to Five Years - Amortized Cost	73,569
After One Year to Five Years - Weighted- Average Yield	1.19%
After Five Years to Ten Years - Amortized Cost	1,311,425
After Five Years to Ten Years - Weighted- Average Yield	2.10%
After Ten Years - Amortized Cost	4,075,575
After Ten Years - Weighted- Average Yield	1.48%
Agency-issued commercial mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	550,269
One Year or Less - Amortized Cost	0
One Year to Five Years - Amortized Cost	0
After Five Years to Ten Years - Amortized Cost	0
After Ten Years - Amortized Cost	550,269
Municipal bonds and notes
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	85,943
One Year or Less - Amortized Cost	3,351
One Year to Five Years - Amortized Cost	26,510
After Five Years to Ten Years - Amortized Cost	43,369
After Ten Years - Amortized Cost	12,713
U.S. agency debentures
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	318,260
Weighted- Average Yield	1.62%
One Year or Less - Amortized Cost	0
One Year or Less - Weighted- Average Yield	1.47%
One Year to Five Years - Amortized Cost	0
After One Year to Five Years - Weighted- Average Yield	1.55%
After Five Years to Ten Years - Amortized Cost	318,260
After Five Years to Ten Years - Weighted- Average Yield	1.89%
After Ten Years - Amortized Cost	0
After Ten Years - Weighted- Average Yield	0.00%
Held-to-maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Weighted- Average Yield	2.25%
One Year or Less - Weighted- Average Yield	5.42%
After One Year to Five Years - Weighted- Average Yield	3.65%
After Five Years to Ten Years - Weighted- Average Yield	2.49%
After Ten Years - Weighted- Average Yield	2.14%
Held-to-maturity Securities [Member] | Agency-issued commercial mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Weighted- Average Yield	2.20%
One Year or Less - Weighted- Average Yield	0.00%
After One Year to Five Years - Weighted- Average Yield	0.00%
After Five Years to Ten Years - Weighted- Average Yield	0.00%
After Ten Years - Weighted- Average Yield	2.20%
Held-to-maturity Securities [Member] | Municipal bonds and notes
Schedule of Held-to-maturity Securities [Line Items]
Weighted- Average Yield	5.99%
One Year or Less - Weighted- Average Yield	5.42%
After One Year to Five Years - Weighted- Average Yield	5.80%
After Five Years to Ten Years - Weighted- Average Yield	6.06%
After Ten Years - Weighted- Average Yield	6.29%
Held-to-maturity Securities [Member] | U.S. agency debentures
Schedule of Held-to-maturity Securities [Line Items]
Weighted- Average Yield	2.93%
One Year or Less - Weighted- Average Yield	0.00%
After One Year to Five Years - Weighted- Average Yield	0.00%
After Five Years to Ten Years - Weighted- Average Yield	2.93%
After Ten Years - Weighted- Average Yield	0.00%
Agency-issued collateralized mortgage obligations | Agency-issued mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,051,644
Weighted- Average Yield	2.42%
One Year or Less - Amortized Cost	0
One Year or Less - Weighted- Average Yield	0.00%
One Year to Five Years - Amortized Cost	47,059
After One Year to Five Years - Weighted- Average Yield	2.43%
After Five Years to Ten Years - Amortized Cost	949,796
After Five Years to Ten Years - Weighted- Average Yield	2.19%
After Ten Years - Amortized Cost	2,054,789
After Ten Years - Weighted- Average Yield	2.52%
Variable rate | Agency-issued collateralized mortgage obligations | Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	148,422
One Year or Less - Amortized Cost	0
One Year to Five Years - Amortized Cost	0
After Five Years to Ten Years - Amortized Cost	0
After Ten Years - Amortized Cost	148,422
Fixed rate | Agency-issued collateralized mortgage obligations | Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,309,382
One Year or Less - Amortized Cost	0
One Year to Five Years - Amortized Cost	0
After Five Years to Ten Years - Amortized Cost	0
After Ten Years - Amortized Cost	$ 1,309,382
Held-to-maturity Securities [Member] | Variable rate | Agency-issued collateralized mortgage obligations | Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Weighted- Average Yield	0.65%
One Year or Less - Weighted- Average Yield	0.00%
After One Year to Five Years - Weighted- Average Yield	0.00%
After Five Years to Ten Years - Weighted- Average Yield	0.00%
After Ten Years - Weighted- Average Yield	0.65%
Held-to-maturity Securities [Member] | Fixed rate | Agency-issued collateralized mortgage obligations | Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Weighted- Average Yield	1.64%
One Year or Less - Weighted- Average Yield	0.00%
After One Year to Five Years - Weighted- Average Yield	0.00%
After Five Years to Ten Years - Weighted- Average Yield	0.00%
After Ten Years - Weighted- Average Yield	1.64%
Lower Limit
Schedule of Held-to-maturity Securities [Line Items]
Mortgage-backed securities contractual maturities (in years)	10 years
Upper Limit
Schedule of Held-to-maturity Securities [Line Items]
Mortgage-backed securities contractual maturities (in years)	30 years