Financial Statement Offsetting (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Offsetting [Abstract]
Derivative contracts, Gross Amounts	$ 4,428,245	$ 5,165,613
Derivative contracts, Netting in Consolidated Statement of Financial Condition	(4,165,446)	(4,759,345)
Derivative contracts, Net Amounts in Consolidated Statement of Financial Condition	262,799	406,268
Derivative contracts, Additional Amounts Available for Setoff	0	0
Derivative contracts, Available Collateral	0	0
Derivative contracts, Net Amount	262,799	406,268
Securities borrowing arrangements, Gross Amounts	6,975,136	6,853,103
Securities borrowing arrangements, Netting in Consolidated Statement of Financial Condition	0	0
Securities borrowing arrangements, Net Amounts in Consolidated Statement of Financial Condition	6,975,136	6,853,103
Securities borrowing arrangements, Additional Amounts Available for Setoff	(478,991)	(680,222)
Securities borrowing arrangements, Available Collateral	(667,099)	(1,274,196)
Securities borrowing arrangements, Net Amount	5,829,046	4,898,685
Reverse repurchase agreements, Gross Amounts	14,046,300	14,059,133
Reverse repurchase agreements, Netting in Consolidated Statement of Financial Condition	(10,191,554)	(10,132,275)
Reverse repurchase agreements, Net Amounts in Consolidated Statement of Financial Condition	3,854,746	3,926,858
Reverse repurchase agreements, Additional Amounts Available for Setoff	(83,452)	(634,568)
Reverse repurchase agreements, Available Collateral	(3,745,215)	(3,248,817)
Reverse repurchase agreements, Net Amount	26,079	43,473
Derivative contracts, Gross Amounts	4,476,241	5,220,133
Derivative contracts, Netting in Consolidated Statement of Financial Condition	(4,257,998)	(4,856,618)
Derivative contracts, Net Amounts in Consolidated Statement of Financial Condition	218,243	363,515
Derivative contracts, Additional Amounts Available for Setoff	0	0
Derivative contracts, Available Collateral	0	0
Derivative contracts, Net Amount	218,243	363,515
Securities lending arrangements, Gross Amounts	3,014,300	2,598,487
Securities lending arrangements, Netting in Consolidated Statement of Financial Condition	0	0
Securities lending arrangements, Net Amounts in Consolidated Statement of Financial Condition	3,014,300	2,598,487
Securities lending arrangements, Additional Amounts Available for Setoff	(478,991)	(680,222)
Securities lending arrangements, Available Collateral	(2,499,395)	(1,883,140)
Securities lending arrangements, Net Amount	35,914	35,125
Repurchase agreements, Gross Amounts	20,158,422	20,804,432
Repurchase agreements, Netting in Consolidated Statement of Financial Condition	(10,191,554)	(10,132,275)
Repurchase agreements, Net Amounts in Consolidated Statement of Financial Condition	9,966,868	10,672,157
Repurchase agreements, Additional Amounts Available for Setoff	(83,452)	(634,568)
Repurchase agreements, Available Collateral	(8,068,468)	(8,810,770)
Repurchase agreements, Net Amount	1,814,948	1,226,819
Securities borrowing arrangements, Net Amount, Subject to Review	5,796,100	4,847,400
Securities borrowing arrangements, Collateral Received, Subject to Review	5,613,300	4,694,000
Repurchase agreements, Net Amount, Subject to Review	1,807,200	1,201,900
Repurchase agreements, Collateral Pledged, Subject to Review	$ 1,875,300	$ 1,238,400