Fair Value (Nonrecurring Fair Value Measurements) (Details) - Fair Value, Measurements, Nonrecurring - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets - Gains (Losses)	$ (140)	$ (84)	$ (39)
Nonaccrual loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets - Gains (Losses)	(111)	(76)	(28)
OREO and Foreclosed Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets - Gains (Losses)	(2)	(5)	(7)
Long-lived Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	20	5
Total assets - Gains (Losses)	(27)	(3)	$ (4)
Fair Value of Property or Collateral
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	370	198
Fair Value of Property or Collateral | Nonaccrual loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	332	136
Fair Value of Property or Collateral | OREO and Foreclosed Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 18	$ 57