Fair Value Measurements (Carrying Values And Fair Values Of Financial Instruments Not Measured At Fair Value) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	$ 7,633
Partially-owned insurance companies	454
Total assets	8,087
Short-term debt	1,401
Long-term debt	3,916
Trust preferred securities	446
Total liabilities	5,763
U.S. Treasury and agency
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,083
Foreign
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	964
Corporate securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,275
Mortgage backed-securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,116
States, municipalities, and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,195
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	7,270	8,447
Partially-owned insurance companies	454	352
Total assets	7,724	8,799
Short-term debt	1,401	1,251
Long-term debt	3,360	3,360
Trust preferred securities	309	309
Total liabilities	5,070	4,920
Carrying Value | U.S. Treasury and agency
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,044	1,078
Carrying Value | Foreign
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	910	935
Carrying Value | Corporate securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,133	2,338
Carrying Value | Mortgage backed-securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,028	2,949
Carrying Value | States, municipalities, and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,155	1,147
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	7,633	8,605
Partially-owned insurance companies	454	352
Total assets	8,087	8,957
Short-term debt	1,401	1,251
Long-term debt	3,916	3,823
Trust preferred securities	446	404
Total liabilities	5,763	5,478
Fair Value | U.S. Treasury and agency
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,083	1,126
Fair Value | Foreign
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	964	930
Fair Value | Corporate securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,275	2,337
Fair Value | Mortgage backed-securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,116	3,036
Fair Value | States, municipalities, and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	$ 1,195	$ 1,176