Capital (Excess Capital Stock) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Capital [Line Items]
Mandatorily redeemable capital stock		$ 83	$ 227	$ 138	$ 227
Amount of Excess Stock Repurchased During Period		$ 431	344
Common stock, par value		$ 100
Excess Capital		$ 175		$ 197
Excess Capital Stock and Excess Mandatorily Redeemable Capital Stock, Redemption, Period of Written Notice		15 days
Mandatorily Redeemable Capital Stock, Redemption Period		5 years
Interest Expense on Mandatorily Redeemable Capital Stock	[1]	$ 2	$ 4
Maximum
Capital [Line Items]
Dividends, Cash Declared, Annualized Rate		7.00%
Minimum
Capital [Line Items]
Dividends, Cash Declared, Annualized Rate		5.00%

[1] The Bank excludes interest expense on mandatorily redeemable capital stock from adjusted net interest income in its analysis of financial performance for its two operating segments