Variable Interest Entities (VIEs) (Details)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2015
USD ($)
Jun. 30, 2016
USD ($)
loan
entity
Jun. 30, 2015
USD ($)
Dec. 31, 2015
USD ($)
loan
Dec. 31, 2014
USD ($)
loan
Dec. 31, 2013
USD ($)
HELOC Securitizations            
Private-label Securitizations [Line Items]            
Payments for Legal Settlements       $ 52    
FSTAR 2007-1 Mortgage Securitization            
Securitized Loans [Abstract]            
Number of loans | loan   2,762   3,061 3,624  
Aggregate principal balance   $ 103   $ 117 $ 141  
Variable Interest Entity, Number of Entities | entity   1        
Recurring | Level 3            
Private-label Securitizations [Line Items]            
Sales $ 24   $ 24 52 0 $ 0
Long-term debt | Recurring | Level 3            
Private-label Securitizations [Line Items]            
Sales $ 24   $ 24 $ 52 $ 0 $ 0