Fair Value of Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Assets
Fixed income securities:	$ 58,656	$ 57,839
Equity securities	6,117	5,666
Short-term investments	2,175	4,288
Other investments: Free-standing derivatives	1		$ 1
Separate account assets	3,416	3,393
Counterparty and cash collateral netting	$ (19)	$ (9)
% of total assets at fair value	0.00%	0.00%
Liabilities
Other liabilities: Free-standing derivatives			$ (8)
Counterparty and cash collateral netting	$ 21	$ 28
Counterparty and cash collateral netting as a percent of liabilities measured at fair value	(6.30%)	(8.40%)
U.S. government and agencies
Assets
Fixed income securities:	$ 3,426	$ 3,637
Municipal
Assets
Fixed income securities:	7,855	7,333
Foreign government
Assets
Fixed income securities:	1,047	1,075
Residential mortgage-backed securities (“RMBS”)
Assets
Fixed income securities:	641	728
Commercial mortgage-backed securities (“CMBS”)
Assets
Fixed income securities:	170	270
Redeemable preferred stock
Assets
Fixed income securities:	23	24
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 12,147	$ 12,408
% of total assets at fair value	17.20%	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	$ 57,502	$ 58,161
% of total assets at fair value	81.60%	81.50%
Liabilities
Total liabilities at fair value	$ (70)	$ (68)
Liabilities as a percent of liabilities measured at fair value	20.90%	20.40%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 858	$ 762
% of total assets at fair value	1.20%	1.10%
Liabilities
Total liabilities at fair value	$ (285)	$ (293)
Liabilities as a percent of liabilities measured at fair value	85.10%	87.70%
Recurring
Assets
Other investments: Free-standing derivatives, Counterparty and cash collateral netting	$ (19)	$ (9)
Liabilities
Counterparty and cash collateral netting	21	28
Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities:	2,773	2,918
Equity securities	5,643	5,247
Short-term investments	315	850
Other investments: Free-standing derivatives	0	0
Separate account assets	3,416	3,393
Other assets	0	0
Total assets at fair value	12,147	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:	2,773	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:	55,208	54,363
Equity securities	308	256
Short-term investments	1,860	3,423
Other investments: Free-standing derivatives	126	119
Separate account assets	0	0
Other assets	0	0
Total assets at fair value	57,502	58,161
Liabilities
Other liabilities: Free-standing derivatives	(70)	(68)
Recurring | Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities:	653	719
Recurring | Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities:	7,741	7,208
Recurring | Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities:	32,079	31,414
Recurring | Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities:	11,846	11,846
Recurring | Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities:	1,047	1,075
Recurring | Significant other observable inputs (Level 2) | ABS - CDO
Assets
Fixed income securities:	520	650
Recurring | Significant other observable inputs (Level 2) | ABS - consumer and other
Assets
Fixed income securities:	512	452
Recurring | Significant other observable inputs (Level 2) | Residential mortgage-backed securities (“RMBS”)
Assets
Fixed income securities:	641	727
Recurring | Significant other observable inputs (Level 2) | Commercial mortgage-backed securities (“CMBS”)
Assets
Fixed income securities:	146	248
Recurring | Significant other observable inputs (Level 2) | Redeemable preferred stock
Assets
Fixed income securities:	23	24
Recurring | Significant unobservable inputs (Level 3)
Assets
Fixed income securities:	675	558
Equity securities	166	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	842	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:	114	125
Recurring | Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities:	60	78
Recurring | Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities:	266	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:	91	27
Recurring | Significant unobservable inputs (Level 3) | ABS - consumer and other
Assets
Fixed income securities:	120	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:	24	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	16	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	(285)	(290)
Fair value
Assets
Total assets at fair value	$ 70,488	$ 71,322
% of total assets at fair value	100.00%	100.00%
Liabilities
Total liabilities at fair value	$ (335)	$ (334)
Liabilities as a percent of liabilities measured at fair value	100.00%	100.00%
Limited partnership interests	$ 15	$ 24
Other investments	1
Fair value | Recurring
Assets
Fixed income securities:	58,656	57,839
Equity securities	6,117	5,666
Short-term investments	2,175	4,288
Other investments: Free-standing derivatives	108	111
Separate account assets	3,416	3,393
Other assets	0	1
Total assets at fair value	70,472	71,298
Liabilities
Other liabilities: Free-standing derivatives	(50)	(44)
Fair value | Recurring | U.S. government and agencies
Assets
Fixed income securities:	3,426	3,637
Fair value | Recurring | Municipal
Assets
Fixed income securities:	7,855	7,333
Fair value | Recurring | Corporate - public
Assets
Fixed income securities:	32,139	31,492
Fair value | Recurring | Corporate - privately placed
Assets
Fixed income securities:	12,112	12,109
Fair value | Recurring | Foreign government
Assets
Fixed income securities:	1,047	1,075
Fair value | Recurring | ABS - CDO
Assets
Fixed income securities:	611	677
Fair value | Recurring | ABS - consumer and other
Assets
Fixed income securities:	632	494
Fair value | Recurring | Residential mortgage-backed securities (“RMBS”)
Assets
Fixed income securities:	641	728
Fair value | Recurring | Commercial mortgage-backed securities (“CMBS”)
Assets
Fixed income securities:	170	270
Fair value | Recurring | Redeemable preferred stock
Assets
Fixed income securities:	23	24
Fair value | Non-recurring
Assets
Total assets at fair value	16	24
Fair value | Derivatives embedded in life and annuity contracts | Recurring
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(285)	(290)
Fixed Income Securities Valued Based on Nonbinding Broker Quotes
Assets
Total assets at fair value	367	307
Municipal Not Rated by Third Party Credit Rating Agencies
Assets
Total assets at fair value	$ 68	$ 80