Invested Assets and Related Income - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012 Investment	Dec. 31, 2011
Schedule of Available-For-Sale Securities [Line Items]
Fixed maturities other-than-temporary impairment losses in gross unrealized depreciation		$ 3,000,000
Taxable, Fair value	18,163,000,000	16,973,000,000
Approximate number of individual fixed maturities in unrealized loss position	250
Approximate number of individual equity securities in unrealized loss position	30
Cumulative credit losses recognized in net income	22,000,000	20,000,000
Minimum equity percentage of single issuer used in concentration risk calculation	10.00%
The Corporation's exposure to investments issued by government and government guaranteed obligations of Canada	1,500,000,000	1,600,000,000
Supranational Organization Issued [Member]
Schedule of Available-For-Sale Securities [Line Items]
Taxable, Fair value	$ 517,000,000	$ 471,000,000