Investments - OTTI losses by asset type (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Realized capital gains and losses by asset type
Gross	$ (4)	$ (47)	$ (4)	$ (109)
Included in OCI	0	(3)	(1)	0
Net	(4)	(50)	(5)	(109)
Municipal
Realized capital gains and losses by asset type
Gross	0	(1)	0	(1)
Included in OCI	0	(2)	0	(2)
Net	0	(3)	0	(3)
Corporate
Realized capital gains and losses by asset type
Gross			0	(9)
Included in OCI			0	3
Net			0	(6)
Asset-backed securities (“ABS”)
Realized capital gains and losses by asset type
Gross	(1)	(1)	(1)	(1)
Included in OCI	0	0	0	0
Net	(1)	(1)	(1)	(1)
Residential mortgage-backed securities (“RMBS”)
Realized capital gains and losses by asset type
Gross	(1)	0	(1)	(1)
Included in OCI	0	0	0	(3)
Net	(1)	0	(1)	(4)
Commercial mortgage-backed securities (“CMBS”)
Realized capital gains and losses by asset type
Gross	0	(2)	0	(8)
Included in OCI	0	(1)	(1)	2
Net	0	(3)	(1)	(6)
Fixed income securities
Realized capital gains and losses by asset type
Gross	(2)	(4)	(2)	(20)
Included in OCI	0	(3)	(1)	0
Net	(2)	(7)	(3)	(20)
Equity securities
Realized capital gains and losses by asset type
Gross	0	(32)	0	(68)
Included in OCI	0	0	0	0
Net	0	(32)	0	(68)
Limited partnership interests
Realized capital gains and losses by asset type
Gross	(1)	(9)	(1)	(16)
Included in OCI	0	0	0	0
Net	(1)	(9)	(1)	(16)
Other
Realized capital gains and losses by asset type
Gross	(1)	(2)	(1)	(5)
Included in OCI	0	0	0	0
Net	$ (1)	$ (2)	$ (1)	$ (5)

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=109979856&loc=SL6284422-111562

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Amount before tax of other than temporary impairment loss (OTTI) on investments in available-for-sale and held-to-maturity debt securities, recognized in other comprehensive loss and attributable to parent entity.

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The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

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