Derivatives and Hedging Activities (Derivatives in Statement of Income and Impact on Interest) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income, Federal Home Loan Bank Advances	$ 2,466	$ 2,443	$ 1,589
Interest Income, Debt Securities, Available-for-sale, Operating	506	504	368
Interest Expense, Other Long-term Debt	(2,289)	(2,095)	(1,239)
Net Fair Value Hedge Ineffectiveness	5
Gain (Loss) on Derivative Instruments, Net, Pretax		19	12
Gain (Loss) on Derivative Instruments [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments		203	85
Gains (Losses) on Hedged Items		(200)	(74)
Net Fair Value Hedge Ineffectiveness		3	11
Consolidated Obligation Bonds [Member] | Interest Expense [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	188	(217)	6
Gains (Losses) on Hedged Items	(357)	(2)	5
Gain (Loss) on Fair Value Hedges Recognized in Net Interest Income	(169)	(219)	11
Available-for-sale Securities [Member] | Interest Income [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	(233)	(22)	(93)
Gains (Losses) on Hedged Items	224	4	(2)
Gain (Loss) on Fair Value Hedges Recognized in Net Interest Income	(9)	(18)	(95)
Advances [Member] | Interest Income [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	(223)	47	(70)
Gains (Losses) on Hedged Items	276	7	(3)
Gain (Loss) on Fair Value Hedges Recognized in Net Interest Income	$ 53	$ 54	$ (73)