Investments (details) - OTTI Rollforward - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Roll-forward of the credit losses on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in other comprehensive income (loss) [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	$ 83	$ 99
Additions for OTTI securities where no credit losses were previously recognized	13	2
Reductions due to sales/defaults of credit-impaired securities	(7)	(10)
Adjustments to book value of credit-impaired securities due to changes in cash flows	(4)	(8)
Cumulative OTTI credit losses recognized for securities still held, end of period	85	83
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Roll-forward of the credit losses on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in other comprehensive income (loss) [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	32	40
Reductions due to sales/defaults of credit-impaired securities		(6)
Adjustments to book value of credit-impaired securities due to changes in cash flows	(1)	(2)
Cumulative OTTI credit losses recognized for securities still held, end of period	31	32
All other corporate bonds [Member]
Roll-forward of the credit losses on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in other comprehensive income (loss) [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	51	59
Additions for OTTI securities where no credit losses were previously recognized	13	2
Reductions due to sales/defaults of credit-impaired securities	(7)	(4)
Adjustments to book value of credit-impaired securities due to changes in cash flows	(3)	(6)
Cumulative OTTI credit losses recognized for securities still held, end of period	$ 54	$ 51

This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which no such other than temporary impairment (OTTI) was previously recognized.

Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsAdditionsNoPreviousImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=SL6284393-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=SL6284393-111563

+ Details

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

- Definition

This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held due to increases in cash flows expected to be collected and recognized over the remaining life of the security.

+ References

+ Details

Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsReductionsCashFlows
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security because of the sale of impaired securities during the period.

+ References

+ Details

Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsReductionsSecuritiesSold
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_OtherDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: