Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fixed maturity securities:
Debt securities	$ 39,546	$ 41,487
Equity securities:
Equity securities	780	695
Estimated Fair Value		695
Short term and other	1,165	1,354
Total assets	41,491	43,536
Other liabilities	(4)	3
Total liabilities	(4)	3
Corporate and other bonds
Fixed maturity securities:
Debt securities	19,814	19,374
States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,748	14,027
Asset-backed
Fixed maturity securities:
Debt securities	8,984	8,086
Common Stock
Equity securities:
Equity securities	148
Estimated Fair Value		27
Preferred stock
Equity securities:
Equity securities	632
Estimated Fair Value		668
Level 1
Fixed maturity securities:
Debt securities	196	128
Equity securities:
Equity securities	192
Estimated Fair Value		91
Short term and other	216	396
Total assets	604	615
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Debt securities	196	128
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	144
Estimated Fair Value		23
Level 1 | Preferred stock
Equity securities:
Equity securities	48
Estimated Fair Value		68
Level 2
Fixed maturity securities:
Debt securities	38,931	40,925
Equity securities:
Equity securities	570
Estimated Fair Value		584
Short term and other	949	958
Total assets	40,450	42,467
Other liabilities	(4)	3
Total liabilities	(4)	3
Level 2 | Corporate and other bonds
Fixed maturity securities:
Debt securities	19,396	19,148
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	10,748	14,026
Level 2 | Asset-backed
Fixed maturity securities:
Debt securities	8,787	7,751
Level 2 | Common Stock
Equity securities:
Equity securities	0
Estimated Fair Value		0
Level 2 | Preferred stock
Equity securities:
Equity securities	570
Estimated Fair Value		584
Level 3
Fixed maturity securities:
Debt securities	419	434
Equity securities:
Equity securities	18
Estimated Fair Value		20
Short term and other	0	0
Total assets	437	454
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Debt securities	222	98
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt securities	0	1
Level 3 | Asset-backed
Fixed maturity securities:
Debt securities	197	335
Level 3 | Common Stock
Equity securities:
Equity securities	4
Estimated Fair Value		4
Level 3 | Preferred stock
Equity securities:
Equity securities	$ 14
Estimated Fair Value		$ 16