Investment Securities (Narrative) (Details) $ in Thousands	6 Months Ended	12 Months Ended			24 Months Ended
	Jun. 30, 2015 USD ($)	Dec. 31, 2016 USD ($) Securities	Dec. 31, 2015 USD ($) Securities	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) Securities
Investment [Line Items]
Interest on securities		$ 203,920	$ 124,086	$ 101,936
Amortized cost of CDO securities sold			$ 574,000
Number of HTM investment securities in an unrealized loss position | Securities		642	187		642
Number of AFS investment securities in an unrealized loss position | Securities		2,398	709		2,398
Amortized Cost of Securities Reclassified from HTM to AFS		$ 0	$ 79,276	$ 0
Carrying value of pledged securities		1,400,000	2,300,000		$ 1,400,000
Available-for-sale Securities, Amortized Cost Basis		13,520,716	7,672,590		13,520,716
Private equity investments prohibited by Volker rule		6,000			6,000
Private Equity Investments		139,000			139,000
Private Equity Investments Sold Prohibited by Volcker Rule		10,000	9,000		19,000
Commitments for private equity and onther noninterest bearing investments		26,000			26,000
Net Fixed Income Securities Gains From Sale of CDOs	$ 137,000
Commitments for Private Equity or Other Non-Interest Bearing Investments Prohibited by the Volcker Rule		$ 4,000			$ 4,000
Available-for-sale Securities [Member]
Investment [Line Items]
Amortized Cost of Securities Reclassified from HTM to AFS			$ 79,000