Derivatives (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	$ 8,551	$ 12,139
Estimated Fair Value Liabilities	4,339	6,921
Maximum Amount of Future Payments under Credit Default Swaps	11,375	10,732
Estimated Fair Value of Credit Default Swaps	271	152
Excess cash collateral received on derivatives	253	164
Securities collateral received which the company is permitted to sell or repledge, amount that has been sold or repledged	0
Derivative Instruments, Gain (Loss) [Line Items]
Net investment gains (losses)	(308)	317	$ 609
Embedded derivatives gains (losses)	799	(181)	200
Derivative Instrument Detail [Abstract]
Net amounts reclassified into net derivatives gains (losses) on discontinued cash flow hedges	$ 13	$ 12	8
Hedging exposure to variability in future cash flows for specific length of time	5 years	5 years
Accumulated Other Comprehensive Income Loss	$ 1,500	$ 2,900
Deferred net gains (losses) expected to be reclassified to earnings	(101)
Amount and Location of Gains (Losses) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (Loss) (Effective Portion)	$ 0		0
Immateriality of cash flow effectiveness	no
Cumulative foreign currency translation gain (loss) recorded in accumulated other comprehensive income (loss) for net investment in foreign operations hedges	$ 300	754
Potential future recoveries available to offset maximum amount of future payments under credit default swaps	27	30
Excess securities collateral provided on derivatives	272	461
Change in fair value of derivatives excluded from the assessment of hedge effectiveness	(40)	(23)	(11)
Over the Counter [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Collateral, Obligation to Return Cash, Offset	4,169	4,244
Excess securities collateral received on derivatives	(108)	(82)
Excess securities collateral provided on derivatives	(305)	(189)
Exchange Cleared [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Collateral, Obligation to Return Cash, Offset	584	1,335
Excess securities collateral provided on derivatives	(522)	(544)
Exchange Traded [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0	0
Excess securities collateral provided on derivatives	(89)	(116)
Nonperformance Risk [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Embedded derivatives gains (losses)	(190)	156	$ 52
Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Estimated Fair Value Assets	75	145
Estimated Fair Value Liabilities	$ (49)	$ (43)