Deferred Policy Acquisition Costs and Value of Business Acquired - VOBA Amortization Expense (Details) $ in Millions	Dec. 31, 2017 USD ($)
Insurance [Abstract]
2018	$ 67
2019	53
2020	48
2021	44
2022	$ 40

No definition available.

Name:	us-gaap_InsuranceAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of amortization expense expected to be recognized during fifth fiscal year following latest fiscal year for present value of future profits of insurance contract acquired in business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6918812&loc=d3e30762-158568

+ Details

Name:	us-gaap_PresentValueOfFutureInsuranceProfitsAmortizationExpenseYearFive
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of amortization expense expected to be recognized during fourth fiscal year following latest fiscal year for present value of future profits of insurance contract acquired in business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 805
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6918812&loc=d3e30762-158568

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

+ Details

Name:	us-gaap_PresentValueOfFutureInsuranceProfitsAmortizationExpenseYearFour
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of amortization expense expected to be recognized during next fiscal year following latest fiscal year for present value of future profits of insurance contract acquired in business combination.

+ References

+ Details

Name:	us-gaap_PresentValueOfFutureInsuranceProfitsAmortizationExpenseYearOne
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of amortization expense expected to be recognized during third fiscal year following latest fiscal year for present value of future profits of insurance contract acquired in business combination.

+ References

+ Details

Name:	us-gaap_PresentValueOfFutureInsuranceProfitsAmortizationExpenseYearThree
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of amortization expense expected to be recognized during second fiscal year following latest fiscal year for present value of future profits of insurance contract acquired in business combination.

+ References

+ Details

Name:	us-gaap_PresentValueOfFutureInsuranceProfitsAmortizationExpenseYearTwo
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant