Fair Value of Assets and Liabilities - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Assets
Fixed income securities	$ 21,541	$ 21,400
Short-term investments	1,284	810
Other investments: Free-standing derivatives	1		$ 1
Separate account assets	3,024	2,783
Derivative asset, fair value, gross liability and obligation to return cash, offset	$ (9)	$ (8)
% of total assets at fair value	0.00%	0.00%
Total	$ 27,975	$ 27,128
Liabilities
Free standing derivative liabilities derivative liability, fair value, gross asset and right to reclaim cash, offset	$ 3	$ 2
% of total liabilities at fair value	(1.10%)	(0.90%)
U.S. government and agencies
Assets
Fixed income securities	$ 538	$ 773
Municipal
Assets
Fixed income securities	2,160	2,195
Foreign government
Assets
Fixed income securities	178	179
RMBS
Assets
Fixed income securities	188	197
CMBS
Assets
Fixed income securities	37	40
Redeemable preferred stock
Assets
Fixed income securities	14	14
Limited partnership interests
Assets
Total assets at fair value	2
Bank loans
Assets
Total assets at fair value	11
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 5,096	$ 4,901
% of total assets at fair value	18.70%	18.60%
Liabilities
Total recurring basis liabilities at fair value	$ 0	$ 0
% of total liabilities at fair value	0.00%	0.00%
Significant other observable inputs (Level 2)
Assets
Total assets at fair value	$ 21,805	$ 21,127
% of total assets at fair value	80.10%	80.20%
Liabilities
Total recurring basis liabilities at fair value	$ (22)	$ (7)
% of total liabilities at fair value	8.20%	3.10%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 325	$ 321
% of total assets at fair value	1.20%	1.20%
Liabilities
Total recurring basis liabilities at fair value	$ (247)	$ (223)
% of total liabilities at fair value	92.90%	97.80%
Investments reported at NAV
Assets
Investments reported at NAV	$ 758	$ 787
Recurring basis
Assets
Other investments: Free-standing derivatives, gross liability and obligation to return cash, offset	(9)	(8)
Derivative asset, fair value, gross liability and obligation to return cash, offset	(9)
Liabilities
Free standing derivative liabilities derivative liability, fair value, gross asset and right to reclaim cash, offset	3	2
Recurring basis | Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities	255	493
Equity securities	1,162	1,182
Short-term investments	655	443
Other investments: Free-standing derivatives	0	0
Separate account assets	3,024	2,783
Total assets at fair value	5,096
Liabilities
Other liabilities: Free-standing derivatives	0	0
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | U.S. government and agencies
Assets
Fixed income securities	255	493
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | Municipal
Assets
Fixed income securities	0	0
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | Corporate - public
Assets
Fixed income securities	0	0
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | Corporate - privately placed
Assets
Fixed income securities	0	0
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | Foreign government
Assets
Fixed income securities	0	0
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | ABS - CDO
Assets
Fixed income securities	0	0
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | ABS - consumer and other
Assets
Fixed income securities	0	0
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | RMBS
Assets
Fixed income securities	0	0
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | CMBS
Assets
Fixed income securities	0	0
Recurring basis | Quoted prices in active markets for identical assets (Level 1) | Redeemable preferred stock
Assets
Fixed income securities	0	0
Recurring basis | Significant other observable inputs (Level 2)
Assets
Fixed income securities	21,081	20,716
Equity securities	16	14
Short-term investments	629	367
Other investments: Free-standing derivatives	79	30
Separate account assets	0	0
Total assets at fair value	21,805
Liabilities
Other liabilities: Free-standing derivatives	(22)	(7)
Recurring basis | Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities	283	280
Recurring basis | Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities	2,120	2,156
Recurring basis | Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities	12,302	11,891
Recurring basis | Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities	5,582	5,552
Recurring basis | Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities	178	179
Recurring basis | Significant other observable inputs (Level 2) | ABS - CDO
Assets
Fixed income securities	23	26
Recurring basis | Significant other observable inputs (Level 2) | ABS - consumer and other
Assets
Fixed income securities	356	381
Recurring basis | Significant other observable inputs (Level 2) | RMBS
Assets
Fixed income securities	188	197
Recurring basis | Significant other observable inputs (Level 2) | CMBS
Assets
Fixed income securities	35	40
Recurring basis | Significant other observable inputs (Level 2) | Redeemable preferred stock
Assets
Fixed income securities	14	14
Recurring basis | Significant unobservable inputs (Level 3)
Assets
Fixed income securities	205	191
Equity securities	106	129
Short-term investments	0	0
Other investments: Free-standing derivatives	1	1
Separate account assets	0	0
Total assets at fair value	312
Liabilities
Other liabilities: Free-standing derivatives	0	0
Recurring basis | Significant unobservable inputs (Level 3) | U.S. government and agencies
Assets
Fixed income securities	0	0
Recurring basis | Significant unobservable inputs (Level 3) | Municipal
Assets
Fixed income securities	40	39
Recurring basis | Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities	35	33
Recurring basis | Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities	97	97
Recurring basis | Significant unobservable inputs (Level 3) | Foreign government
Assets
Fixed income securities	0	0
Recurring basis | Significant unobservable inputs (Level 3) | ABS - CDO
Assets
Fixed income securities	6	6
Recurring basis | Significant unobservable inputs (Level 3) | ABS - consumer and other
Assets
Fixed income securities	25	16
Recurring basis | Significant unobservable inputs (Level 3) | RMBS
Assets
Fixed income securities	0	0
Recurring basis | Significant unobservable inputs (Level 3) | CMBS
Assets
Fixed income securities	2	0
Recurring basis | Significant unobservable inputs (Level 3) | Redeemable preferred stock
Assets
Fixed income securities	0	0
Non-recurring basis | Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	0
Non-recurring basis | Significant other observable inputs (Level 2)
Assets
Total assets at fair value	0
Non-recurring basis | Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	13
Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring basis | Quoted prices in active markets for identical assets (Level 1)
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring basis | Significant other observable inputs (Level 2)
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring basis | Significant unobservable inputs (Level 3)
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(247)	(223)
Fair value
Assets
Total assets at fair value	$ 27,217	$ 26,341
% of total assets at fair value	100.00%	100.00%
Liabilities
Total recurring basis liabilities at fair value	$ (266)	$ (228)
% of total liabilities at fair value	100.00%	100.00%
Fair value | Recurring basis
Assets
Fixed income securities	$ 21,541	$ 21,400
Equity securities	1,284	1,325
Short-term investments	1,284	810
Other investments: Free-standing derivatives	71	23
Separate account assets	3,024	2,783
Total assets at fair value	27,204
Liabilities
Other liabilities: Free-standing derivatives	(19)	(5)
Fair value | Recurring basis | U.S. government and agencies
Assets
Fixed income securities	538	773
Fair value | Recurring basis | Municipal
Assets
Fixed income securities	2,160	2,195
Fair value | Recurring basis | Corporate - public
Assets
Fixed income securities	12,337	11,924
Fair value | Recurring basis | Corporate - privately placed
Assets
Fixed income securities	5,679	5,649
Fair value | Recurring basis | Foreign government
Assets
Fixed income securities	178	179
Fair value | Recurring basis | ABS - CDO
Assets
Fixed income securities	29	32
Fair value | Recurring basis | ABS - consumer and other
Assets
Fixed income securities	381	397
Fair value | Recurring basis | RMBS
Assets
Fixed income securities	188	197
Fair value | Recurring basis | CMBS
Assets
Fixed income securities	37	40
Fair value | Recurring basis | Redeemable preferred stock
Assets
Fixed income securities	14	14
Fair value | Non-recurring basis
Assets
Total assets at fair value	13
Fair value | Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring basis
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	$ (247)	$ (223)