Fair Value of Assets and Liabilities - Assets and liabilities measured at fair value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Fixed income securities	$ 21,400	$ 23,261
Short-term investments	810	725
Other investments:
Other investments: Free-standing derivatives	1	1	$ 1
Counterparty and cash collateral netting	(8)	(3)
Separate account assets		3,422
Derivative asset, fair value	$ (8)	$ (3)
% of total assets at fair value	0.00%	0.00%
Total	$ 27,128
Liabilities
Other liabilities: Free-standing derivatives			$ (3)
Counterparty and cash collateral netting	2	$ 1
Total liabilities at fair value, Counterparty and cash collateral netting	$ 2	$ 1
% of total liabilities at fair value	(0.90%)	(0.30%)
Commitments to invest in limited partnership interests	$ 1,195	$ 1,345
Fair value
Assets
Fixed income securities	21,400	23,261
Equity securities	1,325	1,614
Short-term investments	810	725
Other investments:
Other investments: Free-standing derivatives	23	115
Separate account assets	2,783	3,422
Total assets at fair value	$ 26,341	$ 29,137
% of total assets at fair value	100.00%	100.0103%
Liabilities
Other liabilities: Free-standing derivatives	$ (5)	$ (61)
Total recurring basis liabilities	$ (228)	$ (345)
% of total liabilities at fair value	100.00%	100.00%
Limited partnership interests
Liabilities
Commitments to invest in limited partnership interests	$ 277
U.S. government and agencies
Assets
Fixed income securities	773	$ 804
U.S. government and agencies | Fair value
Assets
Fixed income securities	773	804
Municipal
Assets
Fixed income securities	2,195	2,273
Municipal | Fair value
Assets
Fixed income securities	2,195	2,273
Corporate - public | Fair value
Assets
Fixed income securities	11,924	13,217
Corporate - privately placed | Fair value
Assets
Fixed income securities	5,649	5,919
Foreign government
Assets
Fixed income securities	179	299
Foreign government | Fair value
Assets
Fixed income securities	179	299
ABS - CDO | Fair value
Assets
Fixed income securities	32	48
ABS - consumer and other | Fair value
Assets
Fixed income securities	397	337
RMBS
Assets
Fixed income securities	197	253
RMBS | Fair value
Assets
Fixed income securities	197	253
CMBS
Assets
Fixed income securities	40	97
CMBS | Fair value
Assets
Fixed income securities	40	97
Redeemable preferred stock
Assets
Fixed income securities	14	14
Redeemable preferred stock | Fair value
Assets
Fixed income securities	14	14
Contractholder funds: Derivatives embedded in life and annuity contracts | Fair value
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(223)	(284)
Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities	493	488
Equity securities	1,182	1,508
Short-term investments	443	110
Other investments:
Other investments: Free-standing derivatives	0	0
Separate account assets	2,783	3,422
Total assets at fair value	$ 4,901	$ 5,528
% of total assets at fair value	18.60%	19.00%
Liabilities
Other liabilities: Free-standing derivatives	$ 0	$ 0
Total recurring basis liabilities	$ 0	$ 0
% of total liabilities at fair value	0.00%	0.00%
Quoted prices in active markets for identical assets (Level 1) | U.S. government and agencies
Assets
Fixed income securities	$ 493	$ 488
Quoted prices in active markets for identical assets (Level 1) | Municipal
Assets
Fixed income securities	0	0
Quoted prices in active markets for identical assets (Level 1) | Corporate - public
Assets
Fixed income securities	0	0
Quoted prices in active markets for identical assets (Level 1) | Corporate - privately placed
Assets
Fixed income securities	0	0
Quoted prices in active markets for identical assets (Level 1) | Foreign government
Assets
Fixed income securities	0	0
Quoted prices in active markets for identical assets (Level 1) | ABS - CDO
Assets
Fixed income securities	0	0
Quoted prices in active markets for identical assets (Level 1) | ABS - consumer and other
Assets
Fixed income securities	0	0
Quoted prices in active markets for identical assets (Level 1) | RMBS
Assets
Fixed income securities	0	0
Quoted prices in active markets for identical assets (Level 1) | CMBS
Assets
Fixed income securities	0	0
Quoted prices in active markets for identical assets (Level 1) | Redeemable preferred stock
Assets
Fixed income securities	0	0
Quoted prices in active markets for identical assets (Level 1) | Contractholder funds: Derivatives embedded in life and annuity contracts
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Significant other observable inputs (Level 2)
Assets
Fixed income securities	20,716	22,397
Equity securities	14	16
Short-term investments	367	615
Other investments:
Other investments: Free-standing derivatives	30	117
Separate account assets	0	0
Total assets at fair value	$ 21,127	$ 23,145
% of total assets at fair value	80.20%	79.40%
Liabilities
Other liabilities: Free-standing derivatives	$ (7)	$ (62)
Total recurring basis liabilities	$ (7)	$ (62)
% of total liabilities at fair value	3.10%	18.00%
Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities	$ 280	$ 316
Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities	2,156	2,216
Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities	11,891	13,168
Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities	5,552	5,699
Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities	179	299
Significant other observable inputs (Level 2) | ABS - CDO
Assets
Fixed income securities	26	38
Significant other observable inputs (Level 2) | ABS - consumer and other
Assets
Fixed income securities	381	297
Significant other observable inputs (Level 2) | RMBS
Assets
Fixed income securities	197	253
Significant other observable inputs (Level 2) | CMBS
Assets
Fixed income securities	40	97
Significant other observable inputs (Level 2) | Redeemable preferred stock
Assets
Fixed income securities	14	14
Significant other observable inputs (Level 2) | Contractholder funds: Derivatives embedded in life and annuity contracts
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Significant unobservable inputs (Level 3)
Assets
Fixed income securities	191	376
Equity securities	129	90
Short-term investments	0	0
Other investments:
Other investments: Free-standing derivatives	1	1
Separate account assets	0	0
Total assets at fair value	$ 321	$ 467
% of total assets at fair value	1.20%	1.60%
Liabilities
Other liabilities: Free-standing derivatives	$ 0	$ 0
Total recurring basis liabilities	$ (223)	$ (284)
% of total liabilities at fair value	97.80%	82.30%
Significant unobservable inputs (Level 3) | U.S. government and agencies
Assets
Fixed income securities	$ 0	$ 0
Significant unobservable inputs (Level 3) | Municipal
Assets
Fixed income securities	39	57
Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities	33	49
Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities	97	220
Significant unobservable inputs (Level 3) | Foreign government
Assets
Fixed income securities	0	0
Significant unobservable inputs (Level 3) | ABS - CDO
Assets
Fixed income securities	6	10
Significant unobservable inputs (Level 3) | ABS - consumer and other
Assets
Fixed income securities	16	40
Significant unobservable inputs (Level 3) | RMBS
Assets
Fixed income securities	0	0
Significant unobservable inputs (Level 3) | CMBS
Assets
Fixed income securities	0	0
Significant unobservable inputs (Level 3) | Redeemable preferred stock
Assets
Fixed income securities	0	0
Significant unobservable inputs (Level 3) | Contractholder funds: Derivatives embedded in life and annuity contracts
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(223)	$ (284)
Fair Value Measured at Net Asset Value Per Share [Member]
Other investments:
Investments reported at NAV	$ 787
Minimum | Limited partnership interests
Fair value of assets and liabilities measured on recurring and non-recurring basis
Useful life	10 years
Distribution and proceed period	4 years
Maximum | Limited partnership interests
Fair value of assets and liabilities measured on recurring and non-recurring basis
Useful life	12 years
Distribution and proceed period	9 years