Offsetting Assets and Liabilities (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Offsetting Footnotes [Abstract]
Interest Payable Excluded From Gross Amounts of Derivatives	$ 1,000,000	$ 3,000,000
Securities Borrowed, Transacted Through Clearing Company	52,000,000	34,000,000
Securities Loaned, Transacted Through Clearing Company	698,000,000	722,000,000
Derivative Asset, Not Subject to Master Netting Arrangement	8,000,000	10,000,000
Derivative Liability, Not Subject to Master Netting Arrangement	100,000,000	44,000,000
Offsetting Assets [Abstract]
Securities Borrowed, Gross	186,000,000	120,000,000
Securities Borrowed, Liability	0	0
Securities Borrowed	186,000,000	120,000,000
Securities Borrowed, Financial Instruments, Not Offset	(144,000,000)	(94,000,000)
Securities Borrowed, Collateral Received	(33,000,000)	(18,000,000)
Securities Borrowed, Amount Offset Against Collateral	9,000,000	8,000,000
Derivative Asset, Securities Borrowed, Gross	186,000,000	120,000,000
Derivative Asset, Securities Borrowed, Liability	0	0
Derivative Asset, Securities Borrowed	186,000,000	120,000,000
Derivative Asset, Securities Borrowed, Financial Instruments Not Offset	(144,000,000)	(94,000,000)
Derivative Asset, Securities Borrowed, Collateral Received	(33,000,000)	(18,000,000)
Derivative Asset, Securities Borrowed Net	9,000,000	8,000,000
Offsetting Liabilities [Abstract]
Securities Loaned, Gross	1,395,000,000	1,535,000,000
Securities Loaned, Asset	0	0
Securities Loaned	1,395,000,000	1,535,000,000
Securities Loaned, Financial Instruments, Not Offset	(144,000,000)	(94,000,000)
Securities Loaned, Collateral Pledged	(1,160,000,000)	(1,314,000,000)
Securities Loaned, Amount Offset Against Collateral	91,000,000	127,000,000
Securities Sold under Agreements to Repurchase, Gross		82,000,000
Securities Sold under Agreements to Repurchase, Asset		0
Securities sold under agreements to repurchase		82,000,000
Securities Sold under Agreements to Repurchase, Financial Instruments Not Offset		0
Securities Sold under Agreements to Repurchase, Collateral Pledged		(81,000,000)
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral		1,000,000
Derivative Liability, Fair Value, Gross Liability	31,000,000	11,000,000
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Liability	31,000,000	11,000,000
Derivative Liability, Financial Instruments, Not Offset	0	0
Derivative Liability, Collateral Pledged	(31,000,000)	(11,000,000)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Gross	1,426,000,000	1,628,000,000
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Asset	0	0
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned	1,426,000,000	1,628,000,000
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Financial Instruments Not Offset	(144,000,000)	(94,000,000)
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Collateral Pledged	(1,191,000,000)	(1,406,000,000)
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Amount Offset Against Collateral	$ 91,000,000	$ 128,000,000