Investments - Continuous unrealized loss positions (Details) $ in Millions	Dec. 31, 2019 USD ($) contract	Dec. 31, 2018 USD ($) contract
U.S. government and agencies
Fixed income securities
Number of issues \| contract	31	11
Fair value	$ 1,713	$ 55
Unrealized losses	$ (26)	$ 0
Fixed income securities
Number of issues \| contract	10	38
Fair value	$ 26	$ 364
Unrealized losses	0	(6)
Total unrealized losses	$ (26)	$ (6)
Municipal
Fixed income securities
Number of issues \| contract	307	943
Fair value	$ 576	$ 1,633
Unrealized losses	$ (9)	$ (10)
Fixed income securities
Number of issues \| contract	1	1,147
Fair value	$ 14	$ 1,554
Unrealized losses	(2)	(33)
Total unrealized losses	$ (11)	$ (43)
Corporate
Fixed income securities
Number of issues \| contract	186	1,736
Fair value	$ 1,392	$ 19,243
Unrealized losses	$ (20)	$ (543)
Fixed income securities
Number of issues \| contract	65	645
Fair value	$ 485	$ 8,374
Unrealized losses	(27)	(347)
Total unrealized losses	$ (47)	$ (890)
Foreign government
Fixed income securities
Number of issues \| contract	55	7
Fair value	$ 412	$ 20
Unrealized losses	$ (4)	$ (1)
Fixed income securities
Number of issues \| contract	6	27
Fair value	$ 102	$ 412
Unrealized losses	(1)	(4)
Total unrealized losses	$ (5)	$ (5)
ABS
Fixed income securities
Number of issues \| contract	36	64
Fair value	$ 193	$ 454
Unrealized losses	$ (2)	$ (5)
Fixed income securities
Number of issues \| contract	23	28
Fair value	$ 160	$ 161
Unrealized losses	(4)	(5)
Total unrealized losses	$ (6)	$ (10)
MBS
Fixed income securities
Number of issues \| contract	27	169
Fair value	$ 15	$ 37
Unrealized losses	$ 0	$ 0
Fixed income securities
Number of issues \| contract	123	197
Fair value	$ 14	$ 52
Unrealized losses	(1)	(3)
Total unrealized losses	$ (1)	$ (3)
Fixed income securities
Fixed income securities
Number of issues \| contract	642	2,930
Fair value	$ 4,301	$ 21,442
Unrealized losses	$ (61)	$ (559)
Fixed income securities
Number of issues \| contract	228	2,082
Fair value	$ 801	$ 10,917
Unrealized losses	(35)	(398)
Total unrealized losses	$ (96)	$ (957)
Investment grade fixed income securities
Fixed income securities
Number of issues \| contract	581	2,348
Fair value	$ 3,878	$ 17,485
Unrealized losses	$ (41)	$ (331)
Fixed income securities
Number of issues \| contract	185	2,021
Fair value	$ 594	$ 10,626
Unrealized losses	(20)	(360)
Total unrealized losses	$ (61)	$ (691)
Below investment grade fixed income securities
Fixed income securities
Number of issues \| contract	61	582
Fair value	$ 423	$ 3,957
Unrealized losses	$ (20)	$ (228)
Fixed income securities
Number of issues \| contract	43	61
Fair value	$ 207	$ 291
Unrealized losses	(15)	(38)
Total unrealized losses	$ (35)	$ (266)

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