Investments - Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	$ 78	$ 135	$ 106
Realized - impairments	(73)	(116)	(125)
Total realized gains (losses) on securities	5	19	(19)
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	51	85	66
Realized - impairments	(48)	(72)	(78)
Total realized gains (losses) on securities	3	13	(12)
Change in unrealized	436	72	(411)
Total pretax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	78	135	106
Realized - impairments	(73)	(116)	(125)
Total realized gains (losses) on securities	5	19	(19)
Change in unrealized	441	105	(645)
Fixed maturities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	17	36	19
Realized - impairments	(20)	(38)	(43)
Total realized gains (losses) on securities	(3)	(2)	(24)
Change in unrealized	532	90	(941)
Equity securities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	70	106	94
Realized - impairments	(64)	(93)	(94)
Total realized gains (losses) on securities	6	13	0
Change in unrealized	128	67	(134)
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	(6)	0	(2)
Realized - impairments	(4)	0	(3)
Total realized gains (losses) on securities	(10)	0	(5)
Change in unrealized	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	(3)	(7)	(5)
Realized - impairments	15	15	15
Total realized gains (losses) on securities	12	8	10
Change in unrealized	(219)	(52)	430
Tax effects
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(27)	(48)	(38)
Realized - impairments	25	41	45
Total realized gains (losses) on securities	(2)	(7)	7
Change in unrealized	(5)	(37)	226
Noncontrolling interests
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	0	(2)	(2)
Realized - impairments	0	3	2
Total realized gains (losses) on securities	0	1	0
Change in unrealized	$ 0	$ 4	$ 8

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

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

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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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