Collateralized Transactions (Contractual Maturity) (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending arrangements	$ 3,014,300
Repurchase agreements	20,158,422
Total	23,172,722
Overnight and Continuous [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending arrangements	1,522,475
Repurchase agreements	7,848,231
Total	9,370,706
Up to 30 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending arrangements	0
Repurchase agreements	5,218,059
Total	5,218,059
30 to 90 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending arrangements	973,201
Repurchase agreements	5,291,729
Total	6,264,930
Greater than 90 Days [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities lending arrangements	518,624
Repurchase agreements	1,800,403
Total	$ 2,319,027