Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) (Underwriting Operations)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Underwriting Margin	5.80%	4.10%	6.70%	4.10%
Combined Ratio	94.20%	95.90%	93.30%	95.90%
Personal Lines
Segment Reporting Information [Line Items]
Underwriting Margin	5.90%	4.40%	6.90%	4.00%
Combined Ratio	94.10%	95.60%	93.10%	96.00%
Personal Lines | Agency Channel
Segment Reporting Information [Line Items]
Underwriting Margin	5.60%	2.60%	6.70%	3.90%
Combined Ratio	94.40%	97.40%	93.30%	96.10%
Personal Lines | Direct Channel
Segment Reporting Information [Line Items]
Underwriting Margin	6.30%	6.70%	7.20%	4.10%
Combined Ratio	93.70%	93.30%	92.80%	95.90%
Commercial Auto
Segment Reporting Information [Line Items]
Underwriting Margin	5.90%	1.80%	5.60%	5.00%
Combined Ratio	94.10%	98.20%	94.40%	95.00%