Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	$ 42,207	$ 39,546
Equity securities:
Equity securities	865	780
Short term and other	1,741	1,165
Total assets	44,813	41,491
Other liabilities	7	(4)
Total liabilities	7	(4)
Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	22,728	19,814
States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	10,652	10,748
Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	8,827	8,984
Common Stock
Equity securities:
Equity securities	142	148
Preferred stock
Equity securities:
Equity securities	723	632
Level 1
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	175	196
Equity securities:
Equity securities	189	192
Short term and other	397	216
Total assets	761	604
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	175	196
Level 1 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	0	0
Level 1 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	0	0
Level 1 | Common Stock
Equity securities:
Equity securities	135	144
Level 1 | Preferred stock
Equity securities:
Equity securities	54	48
Level 2
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	41,399	38,931
Equity securities:
Equity securities	658	570
Short term and other	1,344	949
Total assets	43,401	40,450
Other liabilities	7	(4)
Total liabilities	7	(4)
Level 2 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	22,085	19,396
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	10,652	10,748
Level 2 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	8,662	8,787
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Preferred stock
Equity securities:
Equity securities	658	570
Level 3
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	633	419
Equity securities:
Equity securities	18	18
Short term and other	0	0
Total assets	651	437
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	468	222
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	0	0
Level 3 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,126 and $38,085)	165	197
Level 3 | Common Stock
Equity securities:
Equity securities	7	4
Level 3 | Preferred stock
Equity securities:
Equity securities	$ 11	$ 14