Fair Value Measurements (Carrying Values And Fair Values Of Financial Instruments Not Measured At Fair Value) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	$ 7,879
Partially-owned insurance companies	354
Total assets	8,233
Short-term debt	1,402
Long-term debt	3,964
Trust preferred securities	459
Total liabilities	5,825
US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,129
Foreign [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	970
Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,322
Collateralized Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,330
US States and Political Subdivisions Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,128
Financial Instruments Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	7,493	8,447
Partially-owned insurance companies	354	352
Total assets	7,847	8,799
Short-term debt	1,402	1,251
Long-term debt	3,360	3,360
Trust preferred securities	309	309
Total liabilities	5,071	4,920
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	1,084	1,078
Financial Instruments Carrying Value [Member] | Foreign [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	919	935
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	2,182	2,338
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	2,222	2,949
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	1,086	1,147
Financial Instruments Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	7,879	8,605
Partially-owned insurance companies	354	352
Total assets	8,233	8,957
Short-term debt	1,402	1,251
Long-term debt	3,964	3,823
Trust preferred securities	459	404
Total liabilities	5,825	5,478
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	1,129	1,126
Financial Instruments Fair Value [Member] | Foreign [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	970	930
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	2,322	2,337
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	2,330	3,036
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	1,128	1,176
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	7,248
Total assets	7,248
Short-term debt	1,402
Long-term debt	3,964
Trust preferred securities	459
Total liabilities	5,825
Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	514
Fair Value, Inputs, Level 2 [Member] | Foreign [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	970
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,306
Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,330
Fair Value, Inputs, Level 2 [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	1,128
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	16
Partially-owned insurance companies	354
Total assets	370
Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	0
Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	16
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	615
Total assets	615
Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	$ 615