Variable Interest Entities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Variable interest entities
VIE Assets	$ 60,185,851	$ 67,123,261
VIE Liabilities	59,147,068	66,130,592
Investment securities	730,171	807,618
Debt obligations to beneficial interest holders, unpaid principal balances	2,073,229	2,053,229
Interest in VIE	201,823	$ 204,605
Primary beneficiary | Accounting Standards Update 2015-02
Variable interest entities
VIE Assets	180,900
VIE Liabilities	$ 117,500
Not primary beneficiary
Variable interest entities
Number of CDO structures currently in default | item	1
Maximum risk of loss related to VIEs, on fair value basis	$ 15,500
Not primary beneficiary | Accounting Standards Update 2015-02 | Adjustment
Variable interest entities
Maximum risk of loss related to VIEs, on fair value basis	134,500
Interest in VIE	134,500
Commitments on loss	15,500
Not primary beneficiary | Securitization SPEs
Variable interest entities
Debt obligations to beneficial interest holders, unpaid principal balances	$ 8,500,000