Derivatives (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 2,465		$ 2,465		$ 3,603
Derivative Liability, Fair Value, Gross Liability	3,136		3,136		3,883
Maximum Amount of Future Payments under Credit Default Swaps	1,879		1,879		1,891
Estimated Fair Value of Credit Default Swaps	37		37		28
Cash collateral on derivative assets	296		296		$ 3
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring, Net	0	$ 1	9	$ 1
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			18
Embedded derivatives gains (losses)	585	531	$ 1,036	(3,486)
Derivative Instrument Detail [Abstract]
Hedging exposure to variability in future cash flows for specific length of time			2 years		3 years
Accumulated Other Comprehensive Income (Loss)	283		$ 283		$ 397
Cash collateral on derivative liabilities	2		2		25
Securities collateral received which the company is permitted to sell or repledge, amount that has been sold or repledged	0		0
Over the Counter [Member]
Derivatives, Fair Value [Line Items]
Cash collateral on derivative assets	(336)		(336)		(634)
Excess securities collateral received on derivatives	152		152		135
Excess securities collateral provided on derivatives	296		296		108
Exchange Cleared [Member]
Derivatives, Fair Value [Line Items]
Cash collateral on derivative assets	(24)		(24)		(91)
Excess securities collateral provided on derivatives	425		425		630
Exchange Traded [Member]
Derivatives, Fair Value [Line Items]
Cash collateral on derivative assets	0		0		0
Excess securities collateral provided on derivatives	103		103		453
Direct And Assumed Guaranteed Minimum Benefit [Member] | Nonperformance Risk [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Embedded derivatives gains (losses)	525	$ (78)	445	$ 564
Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	68		68		104
Derivative Liability, Fair Value, Gross Liability	$ (8)		$ (8)		$ (49)