Financial Instruments - Derivatives, Offsetting (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Derivative Financial Instruments
Fair value of derivative instruments under collateralized arrangements in a liability position	$ 64	$ 28
Collateral posted on derivative instruments	$ 0	0
Maximum spread on credit default swap agreements before full collateralization is required	2.50%
Fair value of total derivative instruments, Assets	$ 1,166	994
Liabilities included in master netting arrangements	185	139
Obligation to return cash collateral	224	90
Non-cash collateral received	100	40
Net exposure related to derivative assets recorded in the Statement of Financial Position	656	726
Net exposure related to derivative liabilities recorded in the Statement of Financial Position	100	47
Cash collateral rehypothecated	0	0
Other receivables
Derivative Financial Instruments
Right to reclaim cash collateral	0	0
Accounts payable
Derivative Financial Instruments
Obligation to return cash collateral	$ 224	$ 90