Investments (Net Investment Income) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ 4,976	$ 4,876	$ 4,801
Investment expense	(117)	(122)	(103)
Total net investment income	4,859us-gaap_NetInvestmentIncome	4,754us-gaap_NetInvestmentIncome	4,698us-gaap_NetInvestmentIncome
Fixed maturity securities [Member] \| AFS Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	4,041	3,976	3,910
Equity securities [Member] \| AFS Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	9	6	6
Trading securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	125	137	147
Mortgage loans on real estate [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	378	388	397
Real estate [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	7	13	16
Policy loans [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	155	155	163
Cash and invested cash [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	2	3	4
Commercial mortgage loan prepayment and bond makewhole premiums [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	138	117	48
Alternative investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	130	86	125
Consent fees [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	2	4	4
Other investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	(11)	(9)	(19)
Parent Company [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total net investment income	$ 1		$ 1

Amount before accretion (amortization) of purchase discount (premium) of interest income and dividend income on nonoperating securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.7(a),(b))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph a, b

-Article 5

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Amount of expenses related to the generation of investment income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.2)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

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-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 16

-Article 12

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.2)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 3: http://www.xbrl.org/2003/role/presentationRef

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