Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fixed maturity securities:
Debt securities	$ 42,459	$ 39,546
Equity securities:
Equity securities	841	780
Short term and other	1,377	1,165
Total assets	44,677	41,491
Liabilities
Other liabilities	9	(4)
Total liabilities	9	(4)
Corporate and other bonds
Fixed maturity securities:
Debt securities	22,684	19,814
States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,795	10,748
Asset-backed
Fixed maturity securities:
Debt securities	8,980	8,984
Common Stock
Equity securities:
Equity securities	120	148
Preferred stock
Equity securities:
Equity securities	721	632
Level 1
Fixed maturity securities:
Debt securities	161	196
Equity securities:
Equity securities	166	192
Short term and other	288	216
Total assets	615	604
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Debt securities	161	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	114	144
Level 1 | Preferred stock
Equity securities:
Equity securities	52	48
Level 2
Fixed maturity securities:
Debt securities	41,674	38,931
Equity securities:
Equity securities	653	570
Short term and other	1,089	949
Total assets	43,416	40,450
Liabilities
Other liabilities	9	(4)
Total liabilities	9	(4)
Level 2 | Corporate and other bonds
Fixed maturity securities:
Debt securities	22,095	19,396
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,795	10,748
Level 2 | Asset-backed
Fixed maturity securities:
Debt securities	8,784	8,787
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Preferred stock
Equity securities:
Equity securities	653	570
Level 3
Fixed maturity securities:
Debt securities	624	419
Equity securities:
Equity securities	22	18
Short term and other	0	0
Total assets	646	437
Liabilities
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Debt securities	428	222
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	0	0
Level 3 | Asset-backed
Fixed maturity securities:
Debt securities	196	197
Level 3 | Common Stock
Equity securities:
Equity securities	6	4
Level 3 | Preferred stock
Equity securities:
Equity securities	$ 16	$ 14