Investments - Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	$ 17	$ 23	$ 26	$ 57
Realized — impairments	(9)	(39)	(15)	(91)
Realized gains (losses) on securities	8	(16)	11	(34)
Net of tax and noncontrolling interests
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	11	14	17	36
Realized — impairments	(6)	(24)	(10)	(56)
Realized gains (losses) on securities	5	(10)	7	(20)
Change in unrealized	110	219	235	353
Total pretax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	17	23	26	57
Realized — impairments	(9)	(39)	(15)	(91)
Realized gains (losses) on securities	8	(16)	11	(34)
Change in unrealized	170	342	361	552
Fixed maturities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	11	17	16	31
Realized — impairments	(1)	(19)	(1)	(35)
Realized gains (losses) on securities	10	(2)	15	(4)
Change in unrealized	262	584	464	1,037
Equity securities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	8	9	10	32
Realized — impairments	(11)	(26)	(20)	(67)
Realized gains (losses) on securities	(3)	(17)	(10)	(35)
Change in unrealized	20	11	92	(12)
Mortgage loans and other investments
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	0	0	3	0
Realized — impairments	0	0	0	0
Realized gains (losses) on securities	0	0	3	0
Change in unrealized	0	0	0	0
Other, Including DPAC and reserves on annuities and long-term care
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(2)	(3)	(3)	(6)
Realized — impairments	3	6	6	11
Realized gains (losses) on securities	1	3	3	5
Change in unrealized	(112)	(253)	(195)	(473)
Tax effects
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(6)	(8)	(9)	(20)
Realized — impairments	3	14	5	33
Realized gains (losses) on securities	(3)	6	(4)	13
Change in unrealized	(60)	(119)	(126)	(193)
Noncontrolling interests
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	0	(1)	0	(1)
Realized — impairments	0	1	0	2
Realized gains (losses) on securities	0	0	0	1
Change in unrealized	$ 0	$ (4)	$ 0	$ (6)

Change in unrealized appreciation depreciation.

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- Definition

Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments.

+ References

No definition available.

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- Definition

This item represents the total realized gain (loss) included in earnings for the period as a result of selling marketable securities categorized as trading, available-for-sale, or held-to-maturity. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ 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 210.5-03.7(c))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27405-111563

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- Definition

This item represents the total realized gain (loss) included in earnings for the period as a result of selling marketable securities categorized as trading, available-for-sale, or held-to-maturity.

+ References

No definition available.

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The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=82896770&loc=SL6284422-111562

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