Fair Value (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Priced via internal modeling
Fair value by pricing source
Securities priced via internal modeling as a percentage of total portfolio	0.60%
Fixed maturities | Priced via internal modeling
Fair value by pricing source
Number of securities	11
Common stock | Priced via internal modeling
Fair value by pricing source
Number of securities	3
Total
Fair value by pricing source
Total available-for-sale securities and trading securities	10,764
Total | Indemnity
Fair value by pricing source
Total available-for-sale securities and trading securities	600
Total | Indemnity | Fixed maturities
Fair value by pricing source
Total available-for-sale securities and trading securities	548
Total | Indemnity | Fixed maturities | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	542
Total | Indemnity | Fixed maturities | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	2
Total | Indemnity | Fixed maturities | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	4
Total | Indemnity | Preferred stock
Fair value by pricing source
Total available-for-sale securities and trading securities	25
Total | Indemnity | Preferred stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	23
Total | Indemnity | Preferred stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	2
Total | Indemnity | Preferred stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Total | Indemnity | Common stock
Fair value by pricing source
Total available-for-sale securities and trading securities	27
Total | Indemnity | Common stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	27
Total | Indemnity | Common stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Total | Indemnity | Common stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Total | Exchange
Fair value by pricing source
Total available-for-sale securities and trading securities	10,164
Total | Exchange | Fixed maturities
Fair value by pricing source
Total available-for-sale securities and trading securities	7,292
Total | Exchange | Fixed maturities | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	7,158
Total | Exchange | Fixed maturities | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	84
Total | Exchange | Fixed maturities | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	50
Total | Exchange | Preferred stock
Fair value by pricing source
Total available-for-sale securities and trading securities	564
Total | Exchange | Preferred stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	528
Total | Exchange | Preferred stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	36
Total | Exchange | Preferred stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Total | Exchange | Common stock
Fair value by pricing source
Total available-for-sale securities and trading securities	2,308
Total | Exchange | Common stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	2,296
Total | Exchange | Common stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Total | Exchange | Common stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	12
Level 1
Fair value by pricing source
Total available-for-sale securities and trading securities	2,547
Level 1 | Indemnity
Fair value by pricing source
Total available-for-sale securities and trading securities	37
Level 1 | Indemnity | Fixed maturities
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Indemnity | Fixed maturities | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Indemnity | Fixed maturities | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Indemnity | Fixed maturities | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Indemnity | Preferred stock
Fair value by pricing source
Total available-for-sale securities and trading securities	10
Level 1 | Indemnity | Preferred stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	10
Level 1 | Indemnity | Preferred stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Indemnity | Preferred stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Indemnity | Common stock
Fair value by pricing source
Total available-for-sale securities and trading securities	27
Level 1 | Indemnity | Common stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	27
Level 1 | Indemnity | Common stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Indemnity | Common stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Exchange
Fair value by pricing source
Total available-for-sale securities and trading securities	2,510
Level 1 | Exchange | Fixed maturities
Fair value by pricing source
Total available-for-sale securities and trading securities	26
Level 1 | Exchange | Fixed maturities | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	26
Level 1 | Exchange | Fixed maturities | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Exchange | Fixed maturities | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Exchange | Preferred stock
Fair value by pricing source
Total available-for-sale securities and trading securities	188
Level 1 | Exchange | Preferred stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	188
Level 1 | Exchange | Preferred stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Exchange | Preferred stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Exchange | Common stock
Fair value by pricing source
Total available-for-sale securities and trading securities	2,296
Level 1 | Exchange | Common stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	2,296
Level 1 | Exchange | Common stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 1 | Exchange | Common stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2
Fair value by pricing source
Total available-for-sale securities and trading securities	8,146
Level 2 | Indemnity
Fair value by pricing source
Total available-for-sale securities and trading securities	559
Level 2 | Indemnity | Fixed maturities
Fair value by pricing source
Total available-for-sale securities and trading securities	544
Level 2 | Indemnity | Fixed maturities | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	542
Level 2 | Indemnity | Fixed maturities | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	2
Level 2 | Indemnity | Fixed maturities | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Indemnity | Preferred stock
Fair value by pricing source
Total available-for-sale securities and trading securities	15
Level 2 | Indemnity | Preferred stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	13
Level 2 | Indemnity | Preferred stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	2
Level 2 | Indemnity | Preferred stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Indemnity | Common stock
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Indemnity | Common stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Indemnity | Common stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Indemnity | Common stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Exchange
Fair value by pricing source
Total available-for-sale securities and trading securities	7,587
Level 2 | Exchange | Fixed maturities
Fair value by pricing source
Total available-for-sale securities and trading securities	7,216
Level 2 | Exchange | Fixed maturities | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	7,132
Level 2 | Exchange | Fixed maturities | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	84
Level 2 | Exchange | Fixed maturities | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Exchange | Preferred stock
Fair value by pricing source
Total available-for-sale securities and trading securities	371
Level 2 | Exchange | Preferred stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	340
Level 2 | Exchange | Preferred stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	31
Level 2 | Exchange | Preferred stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Exchange | Common stock
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Exchange | Common stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Exchange | Common stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 2 | Exchange | Common stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3
Fair value by pricing source
Total available-for-sale securities and trading securities	71
Level 3 | Indemnity
Fair value by pricing source
Total available-for-sale securities and trading securities	4
Level 3 | Indemnity | Fixed maturities
Fair value by pricing source
Total available-for-sale securities and trading securities	4
Level 3 | Indemnity | Fixed maturities | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Indemnity | Fixed maturities | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Indemnity | Fixed maturities | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	4
Level 3 | Indemnity | Preferred stock
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Indemnity | Preferred stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Indemnity | Preferred stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Indemnity | Preferred stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Indemnity | Common stock
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Indemnity | Common stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Indemnity | Common stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Indemnity | Common stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Exchange
Fair value by pricing source
Total available-for-sale securities and trading securities	67
Level 3 | Exchange | Fixed maturities
Fair value by pricing source
Total available-for-sale securities and trading securities	50
Level 3 | Exchange | Fixed maturities | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Exchange | Fixed maturities | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Exchange | Fixed maturities | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	50
Level 3 | Exchange | Preferred stock
Fair value by pricing source
Total available-for-sale securities and trading securities	5
Level 3 | Exchange | Preferred stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Exchange | Preferred stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	5
Level 3 | Exchange | Preferred stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Exchange | Common stock
Fair value by pricing source
Total available-for-sale securities and trading securities	12
Level 3 | Exchange | Common stock | Priced via pricing services
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Exchange | Common stock | Priced via market comparables/non-binding broker quote
Fair value by pricing source
Total available-for-sale securities and trading securities	0
Level 3 | Exchange | Common stock | Priced via internal modeling
Fair value by pricing source
Total available-for-sale securities and trading securities	12