Fair Value Measurements (Carrying Values And Fair Values Of Financial Instruments Not Measured At Fair Value) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	$ 6,080	$ 6,263
Partially-owned insurance companies	466	470
Total assets	6,546	6,733
Short-term debt	1,907	1,913
Long-term debt	4,139	4,088
Trust preferred securities	452	438
Total liabilities	6,498	6,439
Financial Instruments Fair Value [Member] | U.S. Treasury And Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	790	832
Financial Instruments Fair Value [Member] | Foreign [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	874	897
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	1,965	2,005
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	1,306	1,379
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	1,145	1,150
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	595	596
Total assets	595	596
Fair Value, Inputs, Level 1 [Member] | Financial Instruments Fair Value [Member] | U.S. Treasury And Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	595	596
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	5,469	5,652
Total assets	5,469	5,652
Short-term debt	1,907	1,913
Long-term debt	4,139	4,088
Trust preferred securities	452	438
Total liabilities	6,498	6,439
Fair Value, Inputs, Level 2 [Member] | Financial Instruments Fair Value [Member] | U.S. Treasury And Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	195	236
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	874	897
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	1,949	1,990
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	1,306	1,379
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	1,145	1,150
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	16	15
Partially-owned insurance companies	466	470
Total assets	482	485
Fair Value, Inputs, Level 3 [Member] | Financial Instruments Fair Value [Member] | U.S. Treasury And Agency [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	16	15
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	5,887	6,098
Partially-owned insurance companies	466	470
Total assets	6,353	6,568
Short-term debt	1,901	1,901
Long-term debt	3,808	3,807
Trust preferred securities	309	309
Total liabilities	6,018	6,017
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Financial Instruments Carrying Value [Member] | U.S. Treasury And Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	777	820
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	837	864
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	1,876	1,922
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	1,265	1,341
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	$ 1,132	$ 1,151