Financial Statement Offsetting (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Offsetting [Abstract]
Derivative contracts, Gross Amounts	$ 6,197,200	$ 4,428,245
Derivative contracts, Netting in Consolidated Statement of Financial Condition	(5,850,803)	(4,165,446)
Derivative contracts, Net Amounts in Consolidated Statement of Financial Condition	346,397	262,799
Derivative contracts, Additional Amounts Available for Setoff	0	0
Derivative contracts, Available Collateral	0	0
Derivative contracts, Net Amount	346,397	262,799
Securities borrowing arrangements, Gross Amounts	7,347,587	6,975,136
Securities borrowing arrangements, Netting in Consolidated Statement of Financial Condition	0	0
Securities borrowing arrangements, Net Amounts in Consolidated Statement of Financial Condition	7,347,587	6,975,136
Securities borrowing arrangements, Additional Amounts Available for Setoff	(533,115)	(478,991)
Securities borrowing arrangements, Available Collateral	(623,574)	(667,099)
Securities borrowing arrangements, Net Amount	6,190,898	5,829,046
Reverse repurchase agreements, Gross Amounts	10,253,312	14,046,300
Reverse repurchase agreements, Netting in Consolidated Statement of Financial Condition	(6,726,626)	(10,191,554)
Reverse repurchase agreements, Net Amounts in Consolidated Statement of Financial Condition	3,526,686	3,854,746
Reverse repurchase agreements, Additional Amounts Available for Setoff	(151,575)	(83,452)
Reverse repurchase agreements, Available Collateral	(3,345,710)	(3,745,215)
Reverse repurchase agreements, Net Amount	29,401	26,079
Derivative contracts, Gross Amounts	6,227,889	4,476,241
Derivative contracts, Netting in Consolidated Statement of Financial Condition	(5,879,190)	(4,257,998)
Derivative contracts, Net Amounts in Consolidated Statement of Financial Condition	348,699	218,243
Derivative Fair Value of Derivative Liabilities, Additional Amounts Available for Setoff	0	0
Derivative Liabilities Contracts, Available Collateral	0	0
Derivative contracts, Net Amount	348,699	218,243
Securities lending arrangements, Gross Amounts	2,670,611	3,014,300
Securities lending arrangements, Netting in Consolidated Statement of Financial Condition	0	0
Securities lending arrangements, Net Amounts in Consolidated Statement of Financial Condition	2,670,611	3,014,300
Securities lending arrangements, Additional Amounts Available for Setoff	(533,115)	(478,991)
Securities lending arrangements, Available Collateral	(2,096,442)	(2,499,395)
Securities lending arrangements, Net Amount	41,054	35,914
Repurchase agreements, Gross Amounts	14,978,982	20,158,422
Repurchase agreements, Netting in Consolidated Statement of Financial Condition	(6,726,626)	(10,191,554)
Repurchase agreements, Net Amounts in Consolidated Statement of Financial Condition	8,252,356	9,966,868
Repurchase agreements, Additional Amounts Available for Setoff	(151,575)	(83,452)
Repurchase agreements, Available Collateral	(6,323,605)	(8,068,468)
Repurchase agreements, Net Amount	1,777,176	1,814,948
Securities borrowing arrangements, Net Amount, Subject to Review	6,158,200	5,796,100
Securities borrowing arrangements, Collateral Received, Subject to Review	5,970,000	5,613,300
Repurchase agreements, Net Amount, Subject to Review	1,767,000	1,807,200
Repurchase agreements, Collateral Pledged, Subject to Review	$ 1,823,300	$ 1,875,300