Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Corporate obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	0.345%	0.60%
Maturity	21 years 1 month 21 days	21 years 5 months 9 days
Yield	6.08%	7.20%
U.S. agency obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate		6.91%
Maturity		1 year 3 months 29 days
Yield		2.13%
Collateralized debt obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	1.05%	0.86%
Maturity	1 year 6 months 4 days	1 year 6 months 18 days
Yield	5.92%	11.79%
Other commercial asset-backed [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	0.71%	1.41%
Maturity	7 years 10 months 10 days	3 years
Yield	7.50%	4.50%
European ABS transactions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon rate	1.64%	1.56%
Maturity	12 years 4 months 2 days	11 years 11 months 27 days
Yield	4.02%	3.90%

Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail)

12 Months Ended

Dec. 31, 2012

Dec. 31, 2011

Corporate obligations [Member]

0.345%

0.60%

21 years 1 month 21 days

21 years 5 months 9 days