Capital (Concentration) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Capital Stock Outstanding	$ 3,314	$ 3,138
Total Capital Stock, 10% or more
Concentration Risk [Line Items]
Percentage of Total Capital Stock Outstanding	100.00%	100.00%
Certain Members And Certain Nonmembers [Member]
Concentration Risk [Line Items]
Capital Stock Outstanding	$ 788	$ 762
Percentage of Total Capital Stock Outstanding	24.00%	24.00%
Other Borrowers
Concentration Risk [Line Items]
Capital Stock Outstanding	$ 2,526	$ 2,376
Percentage of Total Capital Stock Outstanding	76.00%	76.00%
First Republic Bank [Member]
Concentration Risk [Line Items]
Capital Stock Outstanding	$ 494	$ 368
First Republic Bank [Member] | Total Capital Stock, 10% or more
Concentration Risk [Line Items]
Percentage of Total Capital Stock Outstanding	15.00%	12.00%
MUFG Union Bank, NA [Member]
Concentration Risk [Line Items]
Capital Stock Outstanding	$ 294	$ 394
MUFG Union Bank, NA [Member] | Total Capital Stock, 10% or more
Concentration Risk [Line Items]
Percentage of Total Capital Stock Outstanding	9.00%	12.00%