Derivatives and Hedging Activities (Derivatives in Statement of Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net	$ 5
Derivatives Not Designated as Hedging Instruments, Gain (Loss), Net	(35)
Net (Losses) Gains on Derivatives and Hedging Activities		$ 19	$ 12
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net		3	11
Gain (Loss) on Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives Not Designated as Hedging Instruments, Gain (Loss), Net	(35)	13	(2)
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Other Gain (Loss)	0	3	3
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives Not Designated as Hedging Instruments, Gain (Loss), Net	(34)	16	10
Gain (Loss) on Derivative Instruments [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Net Interest Settlements [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives Not Designated as Hedging Instruments, Gain (Loss), Net	(1)	(3)	(12)
Gain (Loss) on Derivative Instruments [Member] | Mortgage-Backed Securities [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Forward Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives Not Designated as Hedging Instruments, Gain (Loss), Net	(5)	2	(2)
Mortgage Receivable [Member] | Gain (Loss) on Derivative Instruments [Member] | Forward Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives Not Designated as Hedging Instruments, Gain (Loss), Net	$ 5	$ (2)	$ 2