Fair Value of Assets and Liabilities - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Assets
Fixed income securities	$ 21,567	$ 23,261
Equity securities	1,705	1,614
Short-term investments	1,066	725
Other investments: Free-standing derivatives	1		$ 1
Separate account assets	3,247	3,422
Derivative asset, fair value, gross liability and obligation to return cash, offset	$ (3)	$ (3)
% of total assets at fair value	0.00%	0.00%
Total	$ 28,411
Liabilities
Free standing derivative liabilities derivative liability, fair value, gross asset and right to reclaim cash, offset	$ (3)	$ 1
% of total liabilities at fair value	1.00%	(0.30%)
U.S. government and agencies
Assets
Fixed income securities	$ 403	$ 804
Municipal
Assets
Fixed income securities	2,250	2,273
Foreign government
Assets
Fixed income securities	283	299
RMBS
Assets
Fixed income securities	225	253
CMBS
Assets
Fixed income securities	57	97
Redeemable preferred stock
Assets
Fixed income securities	15	14
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 5,345	$ 5,528
% of total assets at fair value	19.30%	19.00%
Liabilities
Total 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	$ 21,867	$ 23,145
% of total assets at fair value	79.00%	79.40%
Liabilities
Total liabilities at fair value	$ (30)	$ (62)
% of total liabilities at fair value	10.40%	18.00%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 462	$ 467
% of total assets at fair value	1.70%	1.60%
Liabilities
Total liabilities at fair value	$ (257)	$ (284)
% of total liabilities at fair value	88.60%	82.30%
Investments reported at NAV
Assets
Investments reported at NAV	$ 740
Recurring basis
Assets
Other investments: Free-standing derivatives, gross liability and obligation to return cash, offset	(3)	$ (3)
Liabilities
Free standing derivative liabilities derivative liability, fair value, gross asset and right to reclaim cash, offset	(3)	1
Recurring basis | Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities	126	488
Equity securities	1,577	1,508
Short-term investments	395	110
Other investments: Free-standing derivatives	0	0
Separate account assets	3,247	3,422
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	126	488
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	21,093	22,397
Equity securities	15	16
Short-term investments	671	615
Other investments: Free-standing derivatives	88	117
Separate account assets	0	0
Liabilities
Other liabilities: Free-standing derivatives	(30)	(62)
Recurring basis | Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities	277	316
Recurring basis | Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities	2,192	2,216
Recurring basis | Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities	12,381	13,168
Recurring basis | Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities	5,337	5,699
Recurring basis | Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities	283	299
Recurring basis | Significant other observable inputs (Level 2) | ABS - CDO
Assets
Fixed income securities	29	38
Recurring basis | Significant other observable inputs (Level 2) | ABS - consumer and other
Assets
Fixed income securities	297	297
Recurring basis | Significant other observable inputs (Level 2) | RMBS
Assets
Fixed income securities	225	253
Recurring basis | Significant other observable inputs (Level 2) | CMBS
Assets
Fixed income securities	57	97
Recurring basis | Significant other observable inputs (Level 2) | Redeemable preferred stock
Assets
Fixed income securities	15	14
Recurring basis | Significant unobservable inputs (Level 3)
Assets
Fixed income securities	348	376
Equity securities	113	90
Short-term investments	0	0
Other investments: Free-standing derivatives	1	1
Separate account assets	0	0
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	58	57
Recurring basis | Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities	47	49
Recurring basis | Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities	187	220
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	9	10
Recurring basis | Significant unobservable inputs (Level 3) | ABS - consumer and other
Assets
Fixed income securities	47	40
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	0	0
Recurring basis | Significant unobservable inputs (Level 3) | Redeemable preferred stock
Assets
Fixed income securities	0	0
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	(257)	(284)
Fair value
Assets
Total assets at fair value	$ 27,671	$ 29,137
% of total assets at fair value	100.00%	100.00%
Liabilities
Total liabilities at fair value	$ (290)	$ (345)
% of total liabilities at fair value	100.00%	100.00%
Fair value | Recurring basis
Assets
Fixed income securities	$ 21,567	$ 23,261
Equity securities	1,705	1,614
Short-term investments	1,066	725
Other investments: Free-standing derivatives	86	115
Separate account assets	3,247	3,422
Liabilities
Other liabilities: Free-standing derivatives	(33)	(61)
Fair value | Recurring basis | U.S. government and agencies
Assets
Fixed income securities	403	804
Fair value | Recurring basis | Municipal
Assets
Fixed income securities	2,250	2,273
Fair value | Recurring basis | Corporate - public
Assets
Fixed income securities	12,428	13,217
Fair value | Recurring basis | Corporate - privately placed
Assets
Fixed income securities	5,524	5,919
Fair value | Recurring basis | Foreign government
Assets
Fixed income securities	283	299
Fair value | Recurring basis | ABS - CDO
Assets
Fixed income securities	38	48
Fair value | Recurring basis | ABS - consumer and other
Assets
Fixed income securities	344	337
Fair value | Recurring basis | RMBS
Assets
Fixed income securities	225	253
Fair value | Recurring basis | CMBS
Assets
Fixed income securities	57	97
Fair value | Recurring basis | Redeemable preferred stock
Assets
Fixed income securities	15	14
Fair value | Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring basis
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	$ (257)	$ (284)