Derivative Financial Instruments - Amounts Related to Cash Flow Hedges (Details) - Interest Rate Contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flow Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI	$ (116)	$ 69	$ 10
Cash Flow Hedges | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) reclassified from AOCI into interest expense	(25)	(12)	(15)
Cash Flow Hedges | Deposits
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI	(42)	15
Cash Flow Hedges | Deposits | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) reclassified from AOCI into interest expense	(1)	(1)
Cash Flow Hedges | Short-term Debt
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI	2	(3)
Cash Flow Hedges | Short-term Debt | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) reclassified from AOCI into interest expense	(10)	1
Cash Flow Hedges | Long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) recognized in OCI	(76)	57
Cash Flow Hedges | Long-term debt | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) reclassified from AOCI into interest expense	(14)	(12)
Fair value hedges | Net interest income
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized	(47)	4	129
Fair value hedges | Long-term debt | Net interest income
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized	(37)	13	148
Fair value hedges | Loans and leases | Net interest income
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized	(2)	(1)	(3)
Fair value hedges | AFS securities | Net interest income
Derivative Instruments, Gain (Loss) [Line Items]
Net income (expense) recognized	$ (8)	$ (8)	$ (16)