Derivative Financial Instruments - Summary of the impacts of the foreign currency contracts in cash flow hedging relationships (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Gain (loss) recognized in OCI on derivatives during the period	$ 1	$ 0	$ 1	$ (2)
Loss recognized in OCI on derivatives during the term of the hedging relationship	(3)	(1)	(3)	(1)
(Loss) gain reclassified from AOCI into income (net investment income) \| Gain reclassified from AOCI into income (net investment income) \| Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Derivative [Line Items]
Investment Income, Net	0	1	0	1
Realized capital gains and losses \| Gain reclassified from AOCI into income (net investment income) \| Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Derivative [Line Items]
Investment Income, Net	$ 3	$ 0	$ 3	$ 0

Amount of gain or loss recognized in other comprehensive income during the term of the relationship on foreign currency derivatives designated as cash flow hedging relationships.

No definition available.

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+ References

No definition available.

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Amount after accretion (amortization) of discount (premium), and investment expense, of interest income and dividend income on nonoperating securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(a),(b))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

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Amount of net unrealized gain (loss) related to the change in fair value of foreign currency exchange rate derivatives designated as cash flow hedging instruments. Recorded in accumulated other comprehensive income to the extent that the cash flow hedge is determined to be effective.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

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