Financial Statement Offsetting (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Offsetting Derivative Assets [Abstract]
Derivative assets contracts, Gross Amounts	$ 3,497,969	$ 4,627,076
Derivative assets contracts, Netting in Consolidated Statement of Financial Condition	(3,318,481)	(4,255,998)
Total derivative assets	179,488	371,078
Derivative assets contracts, Additional Amounts Available for Setoff	0	0
Derivative assets contracts, Available Collateral	0	0
Derivative assets contracts, Net Amount	179,488	371,078
Gross Amounts	7,721,803	7,743,562
Netting in Consolidated Statement of Financial Condition	0	0
Net Amounts in Consolidated Statement of Financial Condition	7,721,803	7,743,562
Additional Amounts Available for Setoff	(966,712)	(710,611)
Available Collateral	(1,032,629)	(647,290)
Net Amount	5,722,462	6,385,661
Reverse repurchase agreements, Gross Amounts	14,858,297	14,083,144
Reverse repurchase agreements, Netting in Consolidated Statement of Financial Condition	(11,168,738)	(10,220,656)
Reverse repurchase agreements, Net Amounts in Consolidated Statement of Financial Condition	3,689,559	3,862,488
Reverse repurchase agreements, Additional Amounts Available for Setoff	(463,973)	(176,275)
Reverse repurchase agreements, Available Collateral	(3,207,147)	(3,591,654)
Reverse repurchase agreements, Net Amount	18,439	94,559
Offsetting Derivative Liabilities [Abstract]
Derivative liabilities contracts, Gross Amounts	3,745,908	4,880,022
Derivative liabilities contacts, Netting in Consolidated Statement of Financial Condition	(3,490,514)	(4,229,213)
Total derivative liability	255,394	650,809
Derivative liabilities contracts, Additional Amounts Available for Setoff	0	0
Derivative liabilities contracts, Available Collateral	0	0
Derivative liabilities contracts, Net Amount	255,394	650,809
Gross Amounts	2,843,911	2,819,132
Netting in Consolidated Statement of Financial Condition	0	0
Net Amounts in Consolidated Statement of Financial Condition	2,843,911	2,819,132
Additional Amounts Available for Setoff	(966,712)	(710,611)
Available Collateral	(1,795,408)	(2,064,299)
Net Amount	81,791	44,222
Repurchase agreements, Gross Amounts	19,829,249	17,012,332
Repurchase agreements, Netting in Consolidated Statement of Financial Condition	(11,168,738)	(10,220,656)
Repurchase agreements, Net Amounts in Consolidated Statement of Financial Condition	8,660,511	6,791,676
Repurchase agreements, Additional Amounts Available for Setoff	(463,973)	(176,275)
Repurchase agreements, Available Collateral	(7,067,512)	(5,780,909)
Repurchase agreements, Net Amount	1,129,026	834,492
Securities borrowing arrangements, subject to review	5,678,600	6,337,500
Securities borrowing arrangements, collateral received, subject to review	5,516,700	6,146,000
Repurchase agreements, subject to review	1,084,400	810,400
Repurchase agreements, collateral pledged, subject to review	$ 1,115,900	$ 834,200