Fair Value Measurements (Assets Measured at Fair Value on a Non-recurring Basis) (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Loans held-for-sale $ 3,352,000,000   $ 3,352,000,000   $ 2,541,000,000
Total assets at fair value 3,432,000,000   3,432,000,000   2,652,000,000
Net gain on loan sales 94,000,000 $ 68,000,000 259,000,000 $ 242,000,000  
Nonrecurring          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Repossessed assets 15,000,000   15,000,000   17,000,000
Total assets at fair value 48,000,000   48,000,000   67,000,000
Fair value losses on repossessed assets 0 1,000,000 2,000,000 2,000,000  
Net gain on loan sales 1,000,000 1,000,000 2,000,000 2,000,000  
Nonrecurring | Interest income on loans          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Fair value losses on loans (less than for $1 million) 1,000,000 1,000,000 1,000,000 1,000,000  
Nonrecurring | Provision for loan losses          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Fair value losses on loans (less than for $1 million) 11,000,000 $ 20,000,000 31,000,000 $ 76,000,000  
Nonrecurring | Residential first mortgage loans          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Loans held-for-sale 10,000,000   10,000,000   8,000,000
Impaired loans held-for-investment 22,000,000   22,000,000   40,000,000
Nonrecurring | Commercial and industrial          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Impaired loans held-for-investment 1,000,000   1,000,000   2,000,000
Nonrecurring | Level 2          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Repossessed assets 0   0   0
Total assets at fair value 10,000,000   10,000,000   8,000,000
Nonrecurring | Level 2 | Residential first mortgage loans          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Loans held-for-sale 10,000,000   10,000,000   8,000,000
Impaired loans held-for-investment 0   0   0
Nonrecurring | Level 2 | Commercial and industrial          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Impaired loans held-for-investment 0   0   0
Nonrecurring | Level 3          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Repossessed assets 15,000,000   15,000,000   17,000,000
Total assets at fair value 38,000,000   38,000,000   59,000,000
Nonrecurring | Level 3 | Residential first mortgage loans          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Loans held-for-sale 0   0   0
Impaired loans held-for-investment 22,000,000   22,000,000   40,000,000
Nonrecurring | Level 3 | Commercial and industrial          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Impaired loans held-for-investment $ 1,000,000   $ 1,000,000   $ 2,000,000