Derivatives (Fair Value Hedges) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Components Excluded from Assessment of Foreign Currency Fair Value Hedge Effectiveness	$ (8)	$ (7)
Net Derivative Gains (Losses) Recognized for Derivatives	(40)	(7)
Net Derivative Gains (Losses) Recognized for Hedged Items	51	13
Ineffectiveness Recognized in Net Derivative Gains (Losses)	11	6
Interest rate swaps \| Fixed Maturity Securities
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	3	1
Net Derivative Gains (Losses) Recognized for Hedged Items	(2)	(1)
Ineffectiveness Recognized in Net Derivative Gains (Losses)	1	0
Interest rate swaps \| Policyholder account balances
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	(213)	(51)
Net Derivative Gains (Losses) Recognized for Hedged Items	212	50
Ineffectiveness Recognized in Net Derivative Gains (Losses)	(1)	(1)
Foreign currency swaps \| Foreign-denominated fixed maturity securities and mortgage loans
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	(27)	(3)
Net Derivative Gains (Losses) Recognized for Hedged Items	27	3
Ineffectiveness Recognized in Net Derivative Gains (Losses)	0	0
Foreign currency swaps \| Foreign-denominated policyholder account balances [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	18	1
Net Derivative Gains (Losses) Recognized for Hedged Items	(18)	2
Ineffectiveness Recognized in Net Derivative Gains (Losses)	0	3
Foreign currency forwards \| Foreign-denominated fixed maturity securities and mortgage loans
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	179	45
Net Derivative Gains (Losses) Recognized for Hedged Items	(168)	(41)
Ineffectiveness Recognized in Net Derivative Gains (Losses)	$ 11	$ 4

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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The net gain (loss) recognized in earnings in the period relating to components of the gain (loss) on foreign currency fair value hedging instruments excluded from the assessment of fair value hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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Amount of gain (loss)recognized in the income statement from the hedging ineffectiveness of a fair value hedge.

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