Financial Statement Offsetting (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Offsetting [Abstract]
Derivative contracts, Assets, Gross Amounts	$ 3,026,779	$ 4,627,076
Derivative contracts, Assets, Netting in Consolidated Statements of Financial Condition	(2,826,763)	(4,255,998)
Derivative contracts, Assets, Net Amounts in Consolidated Statement of Financial Condition	200,016	371,078
Derivative contracts, Assets, Additional Amounts Available for Setoff	0	0
Derivative contracts, Assets, Available Collateral	0	0
Derivative contracts, Asset, Net Amount	200,016	371,078
Securities borrowing arrangements, Gross Amounts	6,886,436	7,743,562
Securities borrowing arrangements, Netting in Consolidated Statement of Financial Condition	0	0
Securities borrowing arrangements, Net Amounts in Consolidated Statement of Financial Condition	6,886,436	7,743,562
Securities borrowing arrangements, Additional Amounts Available for Setoff	(671,142)	(710,611)
Securities borrowing arrangements, Available Collateral	(486,027)	(647,290)
Securities borrowing arrangements, Net Amount	5,729,267	6,385,661
Reverse repurchase agreements, Gross Amounts	13,553,924	14,083,144
Reverse repurchase agreement, Netting in Consolidated Statements of Financial Condition	(9,085,430)	(10,220,656)
Reverse repurchase agreements, Net Amounts in Consolidated Statement of Financial Condition	4,468,494	3,862,488
Reverse repurchase agreements, Additional Amounts Available for Setoff to Resell, Collateral, Obligation to Return Cash	(701,342)	(176,275)
Reverse repurchase agreements, Available Collateral	(3,711,705)	(3,591,654)
Reverse repurchase agreements, Net Amount	55,447	94,559
Derivative contracts, Liabilities, Gross Amounts	3,190,909	4,880,022
Derivative contracts, Liabilities, Netting in Consolidated Statement of Financial Condition	(2,794,432)	(4,229,213)
Derivative contracts, Liabilities, Net Amounts in Consolidated Statement of Financial Condition	396,477	650,809
Derivative Liabilities, Additional Amounts Available for Setoff	0	0
Derivative Liabilities Contracts, Available Collateral	0	0
Derivative contracts, Net Amount	396,477	650,809
Securities lending arrangements, Gross Amounts	2,522,846	2,819,132
Securities lending arrangements, Netting in Consolidated Statement of Financial Condition	0	0
Securities lending arrangements, Net Amounts in Consolidated Statement of Financial Condition	2,522,846	2,819,132
Securities lending arrangements, Additional Amounts Available for Setoff	(671,142)	(710,611)
Securities lending arrangements, Available Collateral	(1,813,403)	(2,064,299)
Securities lending arrangements, Net Amount	38,301	44,222
Repurchase agreements, Gross Amounts	16,400,889	17,012,332
Repurchase agreements, Netting in Consolidated Statement of Financial Condition	(9,085,430)	(10,220,656)
Repurchase agreements, Net Amounts in Consolidated Statement of Financial Condition	7,315,459	6,791,676
Repurchase agreements, Additional Amounts Available for Setoff	(701,342)	(176,275)
Repurchase agreements, Available Collateral	(5,651,398)	(5,780,909)
Repurchase agreements, Net Amount	962,719	834,492
Securities borrowing agreement, subject to review	5,695,300	6,337,500
Securities borrowing agreement, collateral received, subject to review	5,505,200	6,146,000
Repurchase agreement, net amount, subject to review	948,000	810,400
Repurchase agreements, collateral pledged, subject to review	$ 975,500	$ 834,200