Fair Value of Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Assets
Fixed income securities:	$ 59,391	$ 57,839
Equity securities	6,434	5,666
Short-term investments	2,198	4,288
Other investments: Free-standing derivatives	1		$ 1
Separate account assets	3,422	3,393
Counterparty and cash collateral netting	$ (9)	$ (9)
% of total assets at fair value	0.00%	0.00%
Liabilities
Other liabilities: Free-standing derivatives			$ (4)
Counterparty and cash collateral netting	$ 21	$ 28
Counterparty and cash collateral netting as a percent of liabilities measured at fair value	(6.10%)	(8.40%)
U.S. government and agencies
Assets
Fixed income securities:	$ 3,900	$ 3,637
Municipal
Assets
Fixed income securities:	7,794	7,333
Foreign government
Assets
Fixed income securities:	1,093	1,075
Residential mortgage-backed securities (“RMBS”)
Assets
Fixed income securities:	611	728
Commercial mortgage-backed securities (“CMBS”)
Assets
Fixed income securities:	153	270
Redeemable preferred stock
Assets
Fixed income securities:	24	24
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 12,931	$ 12,408
% of total assets at fair value	18.00%	17.40%
Liabilities
Total liabilities at fair value	$ (1)	$ (1)
Liabilities as a percent of liabilities measured at fair value	0.30%	0.30%
Significant other observable inputs (Level 2)
Assets
Total assets at fair value	$ 57,884	$ 58,161
% of total assets at fair value	80.90%	81.50%
Liabilities
Total liabilities at fair value	$ (69)	$ (68)
Liabilities as a percent of liabilities measured at fair value	20.20%	20.40%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 765	$ 762
% of total assets at fair value	1.10%	1.10%
Liabilities
Total liabilities at fair value	$ (292)	$ (293)
Liabilities as a percent of liabilities measured at fair value	85.60%	87.70%
Recurring
Assets
Other investments: Free-standing derivatives, Counterparty and cash collateral netting	$ (9)	$ (9)
Liabilities
Counterparty and cash collateral netting	21	28
Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities:	3,190	2,918
Equity securities	5,938	5,247
Short-term investments	380	850
Other investments: Free-standing derivatives	0	0
Separate account assets	3,422	3,393
Other assets	1	0
Total assets at fair value	12,931	12,408
Liabilities
Other liabilities: Free-standing derivatives	(1)	(1)
Recurring | Quoted prices in active markets for identical assets (Level 1) | U.S. government and agencies
Assets
Fixed income securities:	3,190	2,918
Recurring | Quoted prices in active markets for identical assets (Level 1) | Municipal
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate - public
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate - privately placed
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Foreign government
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | ABS - CDO
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | ABS - consumer and other
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Residential mortgage-backed securities (“RMBS”)
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Commercial mortgage-backed securities (“CMBS”)
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Redeemable preferred stock
Assets
Fixed income securities:	0	0
Recurring | Significant other observable inputs (Level 2)
Assets
Fixed income securities:	55,629	54,363
Equity securities	328	256
Short-term investments	1,818	3,423
Other investments: Free-standing derivatives	109	119
Separate account assets	0	0
Other assets	0	0
Total assets at fair value	57,884	58,161
Liabilities
Other liabilities: Free-standing derivatives	(69)	(68)
Recurring | Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities:	710	719
Recurring | Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities:	7,687	7,208
Recurring | Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities:	32,269	31,414
Recurring | Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities:	11,923	11,846
Recurring | Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities:	1,093	1,075
Recurring | Significant other observable inputs (Level 2) | ABS - CDO
Assets
Fixed income securities:	545	650
Recurring | Significant other observable inputs (Level 2) | ABS - consumer and other
Assets
Fixed income securities:	640	452
Recurring | Significant other observable inputs (Level 2) | Residential mortgage-backed securities (“RMBS”)
Assets
Fixed income securities:	611	727
Recurring | Significant other observable inputs (Level 2) | Commercial mortgage-backed securities (“CMBS”)
Assets
Fixed income securities:	127	248
Recurring | Significant other observable inputs (Level 2) | Redeemable preferred stock
Assets
Fixed income securities:	24	24
Recurring | Significant unobservable inputs (Level 3)
Assets
Fixed income securities:	572	558
Equity securities	168	163
Short-term investments	0	15
Other investments: Free-standing derivatives	1	1
Separate account assets	0	0
Other assets	0	1
Total assets at fair value	741	738
Liabilities
Other liabilities: Free-standing derivatives	0	(3)
Recurring | Significant unobservable inputs (Level 3) | U.S. government and agencies
Assets
Fixed income securities:	0	0
Recurring | Significant unobservable inputs (Level 3) | Municipal
Assets
Fixed income securities:	107	125
Recurring | Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities:	104	78
Recurring | Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities:	250	263
Recurring | Significant unobservable inputs (Level 3) | Foreign government
Assets
Fixed income securities:	0	0
Recurring | Significant unobservable inputs (Level 3) | ABS - CDO
Assets
Fixed income securities:	19	27
Recurring | Significant unobservable inputs (Level 3) | ABS - consumer and other
Assets
Fixed income securities:	66	42
Recurring | Significant unobservable inputs (Level 3) | Residential mortgage-backed securities (“RMBS”)
Assets
Fixed income securities:	0	1
Recurring | Significant unobservable inputs (Level 3) | Commercial mortgage-backed securities (“CMBS”)
Assets
Fixed income securities:	26	22
Recurring | Significant unobservable inputs (Level 3) | Redeemable preferred stock
Assets
Fixed income securities:	0	0
Non-recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	0	0
Non-recurring | Significant other observable inputs (Level 2)
Assets
Total assets at fair value	0	0
Non-recurring | Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	24	24
Derivatives embedded in life and annuity contracts | Recurring | Quoted prices in active markets for identical assets (Level 1)
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Derivatives embedded in life and annuity contracts | Recurring | Significant other observable inputs (Level 2)
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Derivatives embedded in life and annuity contracts | Recurring | Significant unobservable inputs (Level 3)
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(292)	(290)
Fair value
Assets
Total assets at fair value	$ 71,571	$ 71,322
% of total assets at fair value	100.00%	100.00%
Liabilities
Total liabilities at fair value	$ (341)	$ (334)
Liabilities as a percent of liabilities measured at fair value	100.00%	100.00%
Fair value | Recurring
Assets
Fixed income securities:	$ 59,391	$ 57,839
Equity securities	6,434	5,666
Short-term investments	2,198	4,288
Other investments: Free-standing derivatives	101	111
Separate account assets	3,422	3,393
Other assets	1	1
Total assets at fair value	71,547	71,298
Liabilities
Other liabilities: Free-standing derivatives	(49)	(44)
Fair value | Recurring | U.S. government and agencies
Assets
Fixed income securities:	3,900	3,637
Fair value | Recurring | Municipal
Assets
Fixed income securities:	7,794	7,333
Fair value | Recurring | Corporate - public
Assets
Fixed income securities:	32,373	31,492
Fair value | Recurring | Corporate - privately placed
Assets
Fixed income securities:	12,173	12,109
Fair value | Recurring | Foreign government
Assets
Fixed income securities:	1,093	1,075
Fair value | Recurring | ABS - CDO
Assets
Fixed income securities:	564	677
Fair value | Recurring | ABS - consumer and other
Assets
Fixed income securities:	706	494
Fair value | Recurring | Residential mortgage-backed securities (“RMBS”)
Assets
Fixed income securities:	611	728
Fair value | Recurring | Commercial mortgage-backed securities (“CMBS”)
Assets
Fixed income securities:	153	270
Fair value | Recurring | Redeemable preferred stock
Assets
Fixed income securities:	24	24
Fair value | Non-recurring
Assets
Total assets at fair value	24	24
Liabilities
Limited partnership interests	14	24
Mortgages loans	10
Fair value | Derivatives embedded in life and annuity contracts | Recurring
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(292)	(290)
Fixed Income Securities Valued Based on Nonbinding Broker Quotes
Assets
Total assets at fair value	304	307
Municipal Not Rated by Third Party Credit Rating Agencies
Assets
Total assets at fair value	$ 62	$ 80