Shareholders' Equity - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2013 Federal Insurance Company [Member]	Dec. 31, 2013 P&C Group [Member]	Dec. 31, 2012 P&C Group [Member]
Class of Stock [Line Items]
Remaining under the share repurchase authorization	$ 107,000,000
Authorized repurchase of the Corporation's common stock	1,500,000,000
Aggregate statutory capital and surplus		14,700,000,000	15,024,000,000	14,117,000,000
Risk-based capital requirement		4,900,000,000
Dividends paid by domestic property and casualty insurance subsidiaries to parent	1,600,000,000
Maximum dividend distribution that may be made by the property and casualty insurance subsidiaries to parent company during 2014 without prior regulatory approval	$ 2,000,000,000