Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fixed maturity securities:
Debt securities	$ 40,553	$ 39,546
Equity securities:
Equity securities	814	780
Short term and other	1,379	1,165
Total assets	42,746	41,491
Liabilities
Other liabilities	2	(4)
Total liabilities	2	(4)
Corporate and other bonds
Fixed maturity securities:
Debt securities	21,163	19,814
States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,596	10,748
Asset-backed
Fixed maturity securities:
Debt securities	8,794	8,984
Common Stock
Equity securities:
Equity securities	140	148
Preferred stock
Equity securities:
Equity securities	674	632
Level 1
Fixed maturity securities:
Debt securities	203	196
Equity securities:
Equity securities	186	192
Short term and other	253	216
Total assets	642	604
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Debt securities	203	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	136	144
Level 1 | Preferred stock
Equity securities:
Equity securities	50	48
Level 2
Fixed maturity securities:
Debt securities	39,913	38,931
Equity securities:
Equity securities	608	570
Short term and other	1,126	949
Total assets	41,647	40,450
Liabilities
Other liabilities	2	(4)
Total liabilities	2	(4)
Level 2 | Corporate and other bonds
Fixed maturity securities:
Debt securities	20,707	19,396
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,596	10,748
Level 2 | Asset-backed
Fixed maturity securities:
Debt securities	8,610	8,787
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Preferred stock
Equity securities:
Equity securities	608	570
Level 3
Fixed maturity securities:
Debt securities	437	419
Equity securities:
Equity securities	20	18
Short term and other	0	0
Total assets	457	437
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Debt securities	253	222
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	0	0
Level 3 | Asset-backed
Fixed maturity securities:
Debt securities	184	197
Level 3 | Common Stock
Equity securities:
Equity securities	4	4
Level 3 | Preferred stock
Equity securities:
Equity securities	$ 16	$ 14