Quarterly report pursuant to Section 13 or 15(d)

Trading Securities, at Fair Value (Details)

v2.4.1.9
Trading Securities, at Fair Value (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]      
Trading Securities, Cost $ 1,996,644us-gaap_TradingSecuritiesCost   $ 1,996,289us-gaap_TradingSecuritiesCost
Trading securities, at fair value 2,010,000us-gaap_TradingSecurities   1,997,656us-gaap_TradingSecurities
Trading Securities, Gross Unrealized Gain (Loss) 13,356two_TradingSecuritiesGrossUnrealizedGainLoss   1,367two_TradingSecuritiesGrossUnrealizedGainLoss
Proceeds from sales of trading securities 0two_ProceedsfromSalesofTradingSecurities 98,582two_ProceedsfromSalesofTradingSecurities  
Trading Securities, Amortized Cost Sold   98,220two_TradingSecuritiesAmortizedCostSold  
Trading Securities, Realized Gain (Loss)   362us-gaap_TradingSecuritiesRealizedGainLoss  
Trading Securities, Change in Unrealized Holding Gain (Loss) 11,989us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss (229)us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss  
Assets Sold under Agreements to Repurchase, Market Value 14,719,100us-gaap_AssetsSoldUnderAgreementsToRepurchaseMarketValue   14,599,240us-gaap_AssetsSoldUnderAgreementsToRepurchaseMarketValue
US Treasury Securities [Member]      
Schedule of Trading Securities and Other Trading Assets [Line Items]      
Assets Sold under Agreements to Repurchase, Market Value $ 2,010,000us-gaap_AssetsSoldUnderAgreementsToRepurchaseMarketValue
/ us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis
= us-gaap_USTreasurySecuritiesMember
  $ 1,997,656us-gaap_AssetsSoldUnderAgreementsToRepurchaseMarketValue
/ us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis
= us-gaap_USTreasurySecuritiesMember