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Debt Service Coverage Ratio (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]    
Commercial mortgage loans $ 7,217,169us-gaap_LoansReceivableCommercialMortgage $ 6,200,697us-gaap_LoansReceivableCommercialMortgage
Greater than 1.4x    
Financing Receivable, Recorded Investment [Line Items]    
Commercial mortgage loans 5,204,622us-gaap_LoansReceivableCommercialMortgage
/ us-gaap_RangeAxis
= ck0000072499_RangeOneMember		 4,103,809us-gaap_LoansReceivableCommercialMortgage
/ us-gaap_RangeAxis
= ck0000072499_RangeOneMember
1.2x To 1.4x    
Financing Receivable, Recorded Investment [Line Items]    
Commercial mortgage loans 1,208,043us-gaap_LoansReceivableCommercialMortgage
/ us-gaap_RangeAxis
= ck0000072499_RangeTwoMember		 955,230us-gaap_LoansReceivableCommercialMortgage
/ us-gaap_RangeAxis
= ck0000072499_RangeTwoMember
1.0x To 1.2x    
Financing Receivable, Recorded Investment [Line Items]    
Commercial mortgage loans 656,376us-gaap_LoansReceivableCommercialMortgage
/ us-gaap_RangeAxis
= ck0000072499_RangeThreeMember		 858,438us-gaap_LoansReceivableCommercialMortgage
/ us-gaap_RangeAxis
= ck0000072499_RangeThreeMember
Less than 1.0x    
Financing Receivable, Recorded Investment [Line Items]    
Commercial mortgage loans $ 148,128us-gaap_LoansReceivableCommercialMortgage
/ us-gaap_RangeAxis
= ck0000072499_RangeFourMember		 $ 283,220us-gaap_LoansReceivableCommercialMortgage
/ us-gaap_RangeAxis
= ck0000072499_RangeFourMember