Derivatives and Hedging Activities - Cumulative Basis Adjustments on Fair Value Hedges (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Certificate of deposit ($100,000 or more)	$ 100,000	$ 100,000
Long-term Debt [Member] | Interest Rate [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged item	9,363,000,000
Hedge accounting basis adjustment	(6,000,000)
Certificates of Deposit [Member] | Interest Rate [Member]
Derivatives, Fair Value [Line Items]
Certificate of deposit ($100,000 or more)	100,000
Carrying amount of hedged item	343,000,000
Hedge accounting basis adjustment	(1,000,000)
Bank Time Deposits [Member] | Interest Rate [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged item	178,000,000
Hedge accounting basis adjustment	0
Not Designated as Hedging Instrument [Member] | Long-term Debt [Member] | Interest Rate [Member]
Derivatives, Fair Value [Line Items]
Hedge accounting basis adjustment	$ (10,000,000)