Fair Value of Assets and Liabilities - Rollforward of level 3 assets and liabilities held at fair value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Balance at beginning of period	$ 735	$ 973	$ 1,469
Total gains (losses) included in: net income	22	3	5
Total gains (losses) included in: OCI	15	23	(28)
Transfers into Level 3	94	76	59
Transfers out of Level 3	(369)	(559)	(433)
Purchases	533	410	276
Sales	(113)	(79)	(223)
Issues	0	0	0
Settlements	(80)	(112)	(152)
Balance at end of period	837	735	973
Liabilities
Balance at beginning of period	(290)	(299)	(323)
Total gains (losses) included in: net income	0	(5)	(19)
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	(2)	(3)	(2)
Settlements	6	7	7
Balance at end of period	(286)	(290)	(299)
Fair value assets and liabilities measured on recurring basis, gain (loss) included in earnings
Gain (loss) included in earnings	22	8	24
Other investments: Free-standing derivatives	1	1	1
Free-standing derivatives, liabilities		3	8
Assets transferred between Level 1 and Level 2	0	0	0
Liabilities transferred between Level 1 and Level 2	0	0	0
Realized capital gains and losses
Assets
Total gains (losses) included in: net income	4	(9)	(8)
Net investment income
Assets
Total gains (losses) included in: net income	19	12	13
Interest credited to contractholder funds
Assets
Total gains (losses) included in: net income	(10)	(4)	26
Life and annuity contract benefits
Assets
Total gains (losses) included in: net income	9	9	(7)
Contractholder funds: Derivatives embedded in life and annuity contracts
Liabilities
Balance at beginning of period	(290)	(299)	(323)
Total gains (losses) included in: net income	0	(5)	(19)
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	(2)	(3)	(2)
Settlements	6	7	7
Balance at end of period	(286)	(290)	(299)
U.S. government and agencies
Assets
Balance at beginning of period	0	5	6
Total gains (losses) included in: net income		0	0
Total gains (losses) included in: OCI		0	0
Transfers into Level 3		0	0
Transfers out of Level 3		(4)	0
Purchases		0	0
Sales		0	0
Issues		0	0
Settlements		(1)	(1)
Balance at end of period		0	5
Municipal
Assets
Balance at beginning of period	125	161	270
Total gains (losses) included in: net income	(1)	12	(4)
Total gains (losses) included in: OCI	7	(10)	(7)
Transfers into Level 3	0	6	3
Transfers out of Level 3	(6)	(23)	(2)
Purchases	8	22	0
Sales	(29)	(40)	(91)
Issues	0	0	0
Settlements	(3)	(3)	(8)
Balance at end of period	101	125	161
Corporate - public
Assets
Balance at beginning of period	78	46	214
Total gains (losses) included in: net income	0	0	0
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	4	41	0
Transfers out of Level 3	(30)	(43)	(175)
Purchases	60	47	11
Sales	0	(11)	0
Issues	0	0	0
Settlements	(4)	(2)	(4)
Balance at end of period	108	78	46
Corporate - privately placed
Assets
Balance at beginning of period	263	502	677
Total gains (losses) included in: net income	8	15	13
Total gains (losses) included in: OCI	(2)	18	(20)
Transfers into Level 3	30	16	13
Transfers out of Level 3	(49)	(398)	(106)
Purchases	44	181	79
Sales	(30)	(15)	(74)
Issues	0	0	0
Settlements	(40)	(56)	(80)
Balance at end of period	224	263	502
ABS - CDO
Assets
Balance at beginning of period	27	61	104
Total gains (losses) included in: net income	0	1	(1)
Total gains (losses) included in: OCI	6	6	4
Transfers into Level 3	60	10	43
Transfers out of Level 3	(190)	(43)	(52)
Purchases	219	40	0
Sales	0	(3)	(2)
Issues	0	0	0
Settlements	(23)	(45)	(35)
Balance at end of period	99	27	61
ABS - consumer and other
Assets
Balance at beginning of period	42	50	92
Total gains (losses) included in: net income	0	0	(1)
Total gains (losses) included in: OCI	0	(3)	0
Transfers into Level 3	0	3	0
Transfers out of Level 3	(90)	(35)	(98)
Purchases	103	35	70
Sales	0	(5)	(5)
Issues	0	0	0
Settlements	(7)	(3)	(8)
Balance at end of period	48	42	50
RMBS
Assets
Balance at beginning of period	1	1	1
Total gains (losses) included in: net income	0	1	0
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Purchases	0	0	0
Sales	0	(1)	0
Issues	0	0	0
Settlements	(1)	0	0
Balance at end of period	0	1	1
CMBS
Assets
Balance at beginning of period	22	20	23
Total gains (losses) included in: net income	0	0	0
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	(1)	0
Purchases	6	5	12
Sales	0	0	0
Issues	0	0	0
Settlements	(2)	(2)	(15)
Balance at end of period	26	22	20
Fixed income securities
Assets
Balance at beginning of period	558	846	1,387
Total gains (losses) included in: net income	7	29	7
Total gains (losses) included in: OCI	11	11	(23)
Transfers into Level 3	94	76	59
Transfers out of Level 3	(365)	(547)	(433)
Purchases	440	330	172
Sales	(59)	(75)	(172)
Issues	0	0	0
Settlements	(80)	(112)	(151)
Balance at end of period	606	558	846
Equity securities
Assets
Balance at beginning of period	163	133	83
Total gains (losses) included in: net income	13	(32)	(3)
Total gains (losses) included in: OCI	4	12	(5)
Transfers into Level 3	0	0	0
Transfers out of Level 3	(4)	(12)	0
Purchases	48	65	69
Sales	(14)	(4)	(11)
Issues	0	0	0
Settlements	0	1	0
Balance at end of period	210	163	133
Short-term investments
Assets
Balance at beginning of period	15	0	5
Total gains (losses) included in: net income	0	0	0
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Purchases	45	15	35
Sales	(40)	0	(40)
Issues	0	0	0
Settlements	0	0	0
Balance at end of period	20	15	0
Free-standing derivatives, net
Assets
Balance at beginning of period	(2)	(7)	(7)
Total gains (losses) included in: net income	3	6	1
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	0
Settlements	0	(1)	(1)
Balance at end of period	1	(2)	(7)
Other assets
Assets
Balance at beginning of period	1	1	1
Total gains (losses) included in: net income	(1)	0	0
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	0
Settlements	0	0	0
Balance at end of period	$ 0	$ 1	$ 1