Fair Value Measurements (Carrying Values And Fair Values Of Financial Instruments Not Measured At Fair Value) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	$ 89,749	$ 87,321
Short-term debt	1,531	1,251
Long-term debt	3,360	3,360
Trust preferred securities	309	309
Total liabilities	64,318	62,989
Financial Instruments Carrying Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	8,117	8,447
Partially-owned insurance companies	346	352
Total assets	8,463	8,799
Short-term debt	1,531	1,251
Long-term debt	3,360	3,360
Trust preferred securities	309	309
Total liabilities	5,200	4,920
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	1,081	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	941	935
Financial Instruments Carrying Value [Member] | Corporate Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,298	2,338
Financial Instruments Carrying Value [Member] | Mortgage-Backed Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,693	2,949
Financial Instruments Carrying Value [Member] | States, Municipalities, And Political Subdivisions [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	1,104	1,147
Financial Instruments Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	8,348	8,605
Partially-owned insurance companies	346	352
Total assets	8,694	8,957
Short-term debt	1,531	1,251
Long-term debt	3,878	3,823
Trust preferred securities	404	404
Total liabilities	5,813	5,478
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	1,121	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	955	930
Financial Instruments Fair Value [Member] | Corporate Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,354	2,337
Financial Instruments Fair Value [Member] | Mortgage-Backed Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	2,784	3,036
Financial Instruments Fair Value [Member] | States, Municipalities, And Political Subdivisions [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fixed maturities held to maturity	$ 1,134	$ 1,176