Capital (Concentration) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Concentration Risk [Line Items]
Capital Stock Outstanding	$ 3,138	$ 3,176
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	$ 762	$ 729
Percentage of Total Capital Stock Outstanding	24.00%	23.00%
Other Borrowers
Concentration Risk [Line Items]
Capital Stock Outstanding	$ 2,376	$ 2,447
Percentage of Total Capital Stock Outstanding	76.00%	77.00%
MUFG Union Bank, NA [Member]
Concentration Risk [Line Items]
Capital Stock Outstanding	$ 394	$ 456
MUFG Union Bank, NA [Member] | Total Capital Stock, 10% or more
Concentration Risk [Line Items]
Percentage of Total Capital Stock Outstanding	12.00%	14.00%
First Republic Bank [Member]
Concentration Risk [Line Items]
Capital Stock Outstanding	$ 368	$ 273
First Republic Bank [Member] | Total Capital Stock, 10% or more
Concentration Risk [Line Items]
Percentage of Total Capital Stock Outstanding	12.00%	9.00%