Investments (Net Investment Income) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ 5,169	$ 5,032	$ 4,952
Investment expense	(179)	(158)	(125)
Net investment income	4,990	4,874	4,827
Fixed maturity AFS securities [Member] \| AFS Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	4,163	4,138	4,079
Equity AFS securities [Member] \| AFS Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	12	11	9
Trading securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	94	100	107
Mortgage Loans On Real Estate [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	440	422	395
Real estate [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	2	2	4
Policy loans [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	135	140	152
Invested cash [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	11	14	3
Commercial mortgage loan prepayment and bond makewhole premiums [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	139	120	105
Alternative investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	165	75	88
Consent fees [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	6	5	5
Other investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ 2	$ 5	$ 5

Amount, before 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.

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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 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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

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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 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 944
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-16(Column G))
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915

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+ References

No definition available.

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