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Variable Interest Entities (Narrative) (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Variable Interest Entity [Line Items]    
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets $ 62 $ 61
Genesee [Member]    
Variable Interest Entity [Line Items]    
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount 8  
Guarantee of Indebtedness of Others [Member] | Genesee [Member]    
Variable Interest Entity [Line Items]    
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount $ 3