Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Fixed maturity securities:
Debt securities	$ 41,639	$ 39,546
Equity securities:
Equity securities	830	780
Short term and other	1,411	1,165
Total assets	43,880	41,491
Liabilities
Other liabilities	8	(4)
Total liabilities	8	(4)
Corporate and other bonds
Fixed maturity securities:
Debt securities	22,120	19,814
States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,703	10,748
Asset-backed
Fixed maturity securities:
Debt securities	8,816	8,984
Common Stock
Equity securities:
Equity securities	135	148
Preferred stock
Equity securities:
Equity securities	695	632
Level 1
Fixed maturity securities:
Debt securities	152	196
Equity securities:
Equity securities	180	192
Short term and other	359	216
Total assets	691	604
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Debt securities	152	196
Level 1 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	0	0
Level 1 | Asset-backed
Fixed maturity securities:
Debt securities	0	0
Level 1 | Common Stock
Equity securities:
Equity securities	129	144
Level 1 | Preferred stock
Equity securities:
Equity securities	51	48
Level 2
Fixed maturity securities:
Debt securities	40,956	38,931
Equity securities:
Equity securities	628	570
Short term and other	1,052	949
Total assets	42,636	40,450
Liabilities
Other liabilities	8	(4)
Total liabilities	8	(4)
Level 2 | Corporate and other bonds
Fixed maturity securities:
Debt securities	21,630	19,396
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,703	10,748
Level 2 | Asset-backed
Fixed maturity securities:
Debt securities	8,623	8,787
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Preferred stock
Equity securities:
Equity securities	628	570
Level 3
Fixed maturity securities:
Debt securities	531	419
Equity securities:
Equity securities	22	18
Short term and other	0	0
Total assets	553	437
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Debt securities	338	222
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	0	0
Level 3 | Asset-backed
Fixed maturity securities:
Debt securities	193	197
Level 3 | Common Stock
Equity securities:
Equity securities	6	4
Level 3 | Preferred stock
Equity securities:
Equity securities	$ 16	$ 14