Fair Value Measurements (Carrying Values And Fair Values Of Financial Instruments Not Measured At Fair Value) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	$ 6,762	$ 7,633
Partially-owned insurance companies	452	454
Total assets	7,214	8,087
Short-term debt	1,925	1,401
Long-term debt	4,148	3,916
Trust preferred securities	425	446
Total liabilities	6,498	5,763
Financial Instruments Fair Value [Member] | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	876	1,083
Financial Instruments Fair Value [Member] | Foreign [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	905	964
Financial Instruments Fair Value [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,108	2,275
Financial Instruments Fair Value [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,667	2,116
Financial Instruments Fair Value [Member] | US States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,206	1,195
Fair Value, Inputs, Level 1 [Member] | Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	596	619
Total assets	596	619
Fair Value, Inputs, Level 1 [Member] | Financial Instruments Fair Value [Member] | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	596	619
Fair Value, Inputs, Level 2 [Member] | Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	6,149	6,996
Total assets	6,149	6,996
Short-term debt	1,925	1,401
Long-term debt	4,148	3,916
Trust preferred securities	425	446
Total liabilities	6,498	5,763
Fair Value, Inputs, Level 2 [Member] | Financial Instruments Fair Value [Member] | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	280	464
Fair Value, Inputs, Level 2 [Member] | Financial Instruments Fair Value [Member] | Foreign [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	905	964
Fair Value, Inputs, Level 2 [Member] | Financial Instruments Fair Value [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,091	2,257
Fair Value, Inputs, Level 2 [Member] | Financial Instruments Fair Value [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,667	2,116
Fair Value, Inputs, Level 2 [Member] | Financial Instruments Fair Value [Member] | US States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,206	1,195
Fair Value, Inputs, Level 3 [Member] | Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	17	18
Partially-owned insurance companies	452	454
Total assets	469	472
Fair Value, Inputs, Level 3 [Member] | Financial Instruments Fair Value [Member] | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	0	0
Fair Value, Inputs, Level 3 [Member] | Financial Instruments Fair Value [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	17	18
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Financial Instruments Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	6,576	7,270
Partially-owned insurance companies	452	454
Total assets	7,028	7,724
Short-term debt	1,901	1,401
Long-term debt	3,807	3,360
Trust preferred securities	309	309
Total liabilities	6,017	5,070
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Financial Instruments Carrying Value [Member] | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	858	1,044
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Financial Instruments Carrying Value [Member] | Foreign [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	873	910
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Financial Instruments Carrying Value [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,030	2,133
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Financial Instruments Carrying Value [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,615	2,028
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Financial Instruments Carrying Value [Member] | US States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	$ 1,200	$ 1,155