Securities Financing Activities - Contractual Maturities (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	$ 5,080,164
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	3,214,085
Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	232,924
30 - 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	1,633,155
Greater Than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0
U.S. Treasury and other U.S. government agencies
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	3,965,632
U.S. Treasury and other U.S. government agencies | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	3,214,085
U.S. Treasury and other U.S. government agencies | Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	232,924
U.S. Treasury and other U.S. government agencies | 30 - 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	518,623
U.S. Treasury and other U.S. government agencies | Greater Than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0
Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	976,449
Mortgage-backed securities | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0
Mortgage-backed securities | Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0
Mortgage-backed securities | 30 - 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	976,449
Mortgage-backed securities | Greater Than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0
Collateralized mortgage obligations
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	138,083
Collateralized mortgage obligations | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0
Collateralized mortgage obligations | Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	0
Collateralized mortgage obligations | 30 - 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	138,083
Collateralized mortgage obligations | Greater Than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements repurchase	$ 0