Financial Instruments (Offsetting of Financial Assets and Financial Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Derivative Assets [Abstract]
Derivatives - Gross Amounts of Recognized Assets	$ 546	$ 852
Derivatives - Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Derivatives - Net Presented in the Consolidated Balance Sheets	546	852
Derivatives - Financial Instruments	(2)	(1)
Derivatives - Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Received	(93)	(251)
Derivatives - Gross Amounts Not Offset in the Consolidated Balance Sheets - Non-Cash Collateral Received	(303)	(412)
Derivatives - Net Assets Exposed	148	188
Offsetting Securities Purchased under Agreements to Resell and Securities Borrowed [Abstract]
Reverse repurchase agreements - Gross Amounts of Recognized Assets	2,255	2,637
Reverse repurchase agreements - Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Reverse repurchase agreements - Net Presented in the Consolidated Balance Sheets	2,255	2,637
Reverse repurchase agreements - Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0	0
Reverse repurchase agreements - Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Received	0	0
Reverse repurchase agreements - Gross Amounts Not Offset in the Consolidated Balance Sheets - Non-Cash Collateral Received	(2,255)	(2,637)
Reverse repurchase agreements - Net Assets Exposed	0	0
Offsetting Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed [Abstract]
Total - Gross Amounts of Recognized Assets	2,801	3,489
Total - Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Total - Net Presented in the Consolidated Balance Sheets	2,801	3,489
Total - Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(2)	(1)
Total - Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Received	(93)	(251)
Total - Gross Amounts Not Offset in the Consolidated Balance Sheets - Non-Cash Collateral Received	(2,558)	(3,049)
Total - Net Assets Exposed	148	188
Offsetting Derivative Liabilities [Abstract]
Derivatives - Gross Amounts of Recognized Liabilities	10	4
Derivatives - Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Derivatives - Net Presented in the Consolidated Balance Sheets	10	4
Derivatives - Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(2)	(1)
Derivatives - Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	(4)	0
Derivatives - Gross Amounts Not Offset in the Consolidated Balance Sheets - Non-Cash Collateral Pledged	0	0
Derivatives - Net Liabilities	4	3
Offsetting Securities Loaned [Abstract]
Total	3,266	2,778
Amounts related to agreements not included in securities lending in offsetting disclosure	0	0
Securities lending agreements - Net Presented in the Consolidated Balance Sheets	3,266	2,778
Securities lending agreements - Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0	0
Securities lending agreements - Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	0	0
Securities lending agreements - Gross Amounts Not Offset in the Consolidated Balance Sheets - Non-Cash Collateral Pledged	(3,245)	(2,740)
Securities lending agreements - Net Liabilities	21	38
Offsetting Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned [Abstract]
Total - Gross Amounts of Recognized Liabilities	3,276	2,782
Total - Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Total - Net Presented in the Consolidated Balance Sheets	3,276	2,782
Total - Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(2)	(1)
Total - Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	(4)	0
Total - Gross Amounts Not Offset in the Consolidated Balance Sheets - Non-Cash Collateral Pledged	(3,245)	(2,740)
Total - Net Liabilities	25	41
Cash and cash equivalents
Offsetting Securities Purchased under Agreements to Resell and Securities Borrowed [Abstract]
Reverse repurchase agreements - Gross Amounts of Recognized Assets	1,855	1,762
Receivable under reverse repurchase agreements
Offsetting Securities Purchased under Agreements to Resell and Securities Borrowed [Abstract]
Reverse repurchase agreements - Gross Amounts of Recognized Assets	$ 400	$ 875