Investment Assets and Related Income (Details 9) (USD $)	12 Months Ended
	Dec. 31, 2011 Investment	Dec. 31, 2010
Schedule of Available-for-sale Securities [Abstract]
Tax exempt, Fair value	$ 20,211,000,000	$ 19,774,000,000
Taxable, Fair value	16,973,000,000	16,745,000,000
Invested Assets (Textual) [Abstract]
Fixed maturities other-than-temporary impairment losses in gross unrealized depreciation	3,000,000	4,000,000
Approximate number of individual fixed maturity and equity securities in unrealized loss position	380
Approximate number of individual fixed maturities in unrealized loss position	345
Cumulative credit losses recognized in net income	20,000,000	21,000,000
The threshold for the fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state	5.00%
The threshold for the fair value and amortized cost for the foreign government and government agency fixed maturities for each country table	5.00%
Minimum equity percentage of single issuer used in concentration risk calculation	10.00%
Government and government guaranteed obligations of Canada [Member]
Additional Invested Assets (Textual) [Abstract]
The Corporation's exposure to investments issued by government and government guaranteed obligations of Canada	1,600,000,000
Special Revenues Bond [Member]
Schedule of Available-for-sale Securities [Abstract]
Tax exempt, Fair value	12,405,000,000
Municipal and Political Subdivision General Obligation Bonds [Member]
Schedule of Available-for-sale Securities [Abstract]
Tax exempt, Fair value	2,614,000,000
State General Obligation Bonds [Member]
Schedule of Available-for-sale Securities [Abstract]
Tax exempt, Fair value	2,548,000,000
Pre-Refunded Bonds [Member]
Schedule of Available-for-sale Securities [Abstract]
Tax exempt, Fair value	2,644,000,000
Supranational Organization Issued [Member]
Schedule of Available-for-sale Securities [Abstract]
Taxable, Fair value	$ 471,000,000