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Change in Fair Value of Financial Instruments for which the FVO has been Elected (Additional Information) (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Income recognized upon the sale of loans $ 6us-gaap_GainLossOnSalesOfLoansNet $ 9us-gaap_GainLossOnSalesOfLoansNet  
Fair Value, Measurements, Nonrecurring [Member] | Other Assets [Member]      
Asset Impairment Charges 0us-gaap_AssetImpairmentCharges
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_OtherAssetsMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		   64us-gaap_AssetImpairmentCharges
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_OtherAssetsMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value, Measurements, Nonrecurring [Member] | Other Assets [Member] | Land [Member]      
Asset Impairment Charges $ 0us-gaap_AssetImpairmentCharges
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_OtherAssetsMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_LandMember		   $ 5us-gaap_AssetImpairmentCharges
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_OtherAssetsMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
/ us-gaap_InvestmentTypeAxis
= us-gaap_LandMember