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Commitments and Contingencies (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Commitments and Contingencies Disclosure [Line Items]      
Rent expense $ 116,000,000 $ 114,000,000 $ 116,000,000
Standby letters of credit [Member]      
Commitments and Contingencies Disclosure [Line Items]      
Aggregate face amount of letter of credit agreements $ 304,000,000    
Bond Market Fund Litigation [Member]      
Commitments and Contingencies Disclosure [Line Items]      
Alleged minimum percentage of fund assets invested in CMOs and mortgage-backed securities without obtaining shareholder vote 25.00%    
Margin Requirements [Member]      
Commitments and Contingencies Disclosure [Line Items]      
Funds drawn under LOC's $ 0