Fair Value of Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Fixed income securities	$ 57,839	$ 57,948
Equity securities	5,666	5,082
Short-term investments	4,288	2,122
Other investments: Free-standing derivatives	1	1	$ 2
Separate account assets	3,393	3,658
Counterparty and cash collateral netting	$ (9)	$ (13)
Assets as a percent of assets measured at fair value	0.00%	0.00%
Liabilities
Other liabilities: Free-standing derivatives	$ (3)	$ (8)	$ (9)
Counterparty and cash collateral netting	$ 28	$ 7
Counterparty and cash collateral netting as a percent of liabilities measured at fair value	(8.40%)	(2.20%)
Limited partnership interests	$ 24	$ 42
Other investments		13
U.S. government and agencies
Assets
Fixed income securities	3,637	3,922
Municipal
Assets
Fixed income securities	7,333	7,401
Foreign government
Assets
Fixed income securities	1,075	1,033
RMBS
Assets
Fixed income securities	728	947
CMBS
Assets
Fixed income securities	270	466
Redeemable preferred stock
Assets
Fixed income securities	24	25
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 12,408	$ 12,117
Assets as a percent of assets measured at fair value	17.40%	17.60%
Liabilities
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	$ 58,161	$ 55,781
Assets as a percent of assets measured at fair value	81.50%	80.90%
Liabilities
Liabilities as a percent of liabilities measured at fair value	20.40%	7.10%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 762	$ 1,036
Assets as a percent of assets measured at fair value	1.10%	1.50%
Liabilities
Liabilities as a percent of liabilities measured at fair value	87.70%	94.80%
Recurring
Assets
Counterparty and cash collateral netting	$ (9)	$ (13)
Liabilities
Counterparty and cash collateral netting	28	7
Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities	2,918	3,056
Equity securities	5,247	4,786
Short-term investments	850	615
Other investments: Free-standing derivatives	0	0
Separate account assets	3,393	3,658
Other assets	0	2
Total assets at fair value	12,408	12,117
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Other liabilities: Free-standing derivatives	(1)	(1)
Total liabilities at fair value	(1)	(1)
Recurring | Quoted prices in active markets for identical assets (Level 1) | U.S. government and agencies
Assets
Fixed income securities	2,918	3,056
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) | RMBS
Assets
Fixed income securities	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | 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	54,363	54,046
Equity securities	256	163
Short-term investments	3,423	1,507
Other investments: Free-standing derivatives	119	65
Separate account assets	0	0
Other assets	0	0
Total assets at fair value	58,161	55,781
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Other liabilities: Free-standing derivatives	(68)	(23)
Total liabilities at fair value	(68)	(23)
Recurring | Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities	719	861
Recurring | Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities	7,208	7,240
Recurring | Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities	31,414	30,356
Recurring | Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities	11,846	10,923
Recurring | Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities	1,075	1,033
Recurring | Significant other observable inputs (Level 2) | ABS - CDO
Assets
Fixed income securities	650	716
Recurring | Significant other observable inputs (Level 2) | ABS - consumer and other
Assets
Fixed income securities	452	1,500
Recurring | Significant other observable inputs (Level 2) | RMBS
Assets
Fixed income securities	727	946
Recurring | Significant other observable inputs (Level 2) | CMBS
Assets
Fixed income securities	248	446
Recurring | Significant other observable inputs (Level 2) | Redeemable preferred stock
Assets
Fixed income securities	24	25
Recurring | Significant unobservable inputs (Level 3)
Assets
Fixed income securities	558	846
Equity securities	163	133
Short-term investments	15	0
Other investments: Free-standing derivatives	1	1
Separate account assets	0	0
Other assets	1	1
Total assets at fair value	738	981
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(290)	(299)
Other liabilities: Free-standing derivatives	(3)	(8)
Total liabilities at fair value	(293)	(307)
Recurring | Significant unobservable inputs (Level 3) | U.S. government and agencies
Assets
Fixed income securities	0	5
Recurring | Significant unobservable inputs (Level 3) | Municipal
Assets
Fixed income securities	125	161
Recurring | Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities	78	46
Recurring | Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities	263	502
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	27	61
Recurring | Significant unobservable inputs (Level 3) | ABS - consumer and other
Assets
Fixed income securities	42	50
Recurring | Significant unobservable inputs (Level 3) | RMBS
Assets
Fixed income securities	1	1
Recurring | Significant unobservable inputs (Level 3) | CMBS
Assets
Fixed income securities	22	20
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	55
Fair value
Assets
Total assets at fair value	$ 71,322	$ 68,921
Assets as a percent of assets measured at fair value	100.00%	100.00%
Liabilities
Liabilities as a percent of liabilities measured at fair value	100.00%	100.00%
Fair value | Recurring
Assets
Fixed income securities	$ 57,839	$ 57,948
Equity securities	5,666	5,082
Short-term investments	4,288	2,122
Other investments: Free-standing derivatives	111	53
Separate account assets	3,393	3,658
Other assets	1	3
Total assets at fair value	71,298	68,866
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(290)	(299)
Other liabilities: Free-standing derivatives	(44)	(25)
Total liabilities at fair value	(334)	(324)
Fair value | Recurring | U.S. government and agencies
Assets
Fixed income securities	3,637	3,922
Fair value | Recurring | Municipal
Assets
Fixed income securities	7,333	7,401
Fair value | Recurring | Corporate - public
Assets
Fixed income securities	31,492	30,402
Fair value | Recurring | Corporate - privately placed
Assets
Fixed income securities	12,109	11,425
Fair value | Recurring | Foreign government
Assets
Fixed income securities	1,075	1,033
Fair value | Recurring | ABS - CDO
Assets
Fixed income securities	677	777
Fair value | Recurring | ABS - consumer and other
Assets
Fixed income securities	494	1,550
Fair value | Recurring | RMBS
Assets
Fixed income securities	728	947
Fair value | Recurring | CMBS
Assets
Fixed income securities	270	466
Fair value | Recurring | Redeemable preferred stock
Assets
Fixed income securities	24	25
Fair value | Non-recurring
Assets
Total assets at fair value	$ 24	$ 55