Derivatives (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 1,846		$ 1,846		$ 2,244
Derivative Liability, Fair Value, Gross Liability	3,304		3,304		3,129
Maximum Amount of Future Payments under Credit Default Swaps	1,872		1,872		1,878
Cash collateral on derivative assets	39		39		$ 93
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring, Net		$ 0	$ 0	$ 9
Derivative Instrument Detail [Abstract]
Hedging exposure to variability in future cash flows for specific length of time			0 years		2 years
Accumulated Other Comprehensive Income (Loss)	194		$ 194		$ 231
Cash collateral on derivative liabilities	0		0		5
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	(228)		(228)		(247)
Excess securities collateral received on derivatives	69		69		337
Excess securities collateral provided on derivatives	307		307		471
Exchange Cleared [Member]
Derivatives, Fair Value [Line Items]
Cash collateral on derivative assets	(20)		(20)		(27)
Excess securities collateral provided on derivatives	79		79		426
Exchange Traded [Member]
Derivatives, Fair Value [Line Items]
Excess securities collateral provided on derivatives	105		105		118
Direct And Assumed Guaranteed Minimum Benefit [Member] | Nonperformance Risk [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Embedded derivatives gains (losses)	(164)	$ 525	(121)	$ 445
Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	68		68		47
Derivative Liability, Fair Value, Gross Liability	$ (8)		$ (8)		$ (9)