Subsequent Events (Subsequent Event - Additional Information) (Detail) - USD ($) $ in Millions		12 Months Ended
	Jan. 31, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Face amount of notes issued or redeemed		$ 1,370
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed		100.00%
Debt Instrument, Redemption, Description		The 2.25% senior fixed-rate notes will be redeemable at the Bank’s option, in whole or in part, at any time or from time to time, on or after July 31, 2020, and prior to January 4, 2027 (the “Applicable Par Call Date”), in each case at a redemption price, plus accrued and unpaid interest thereon, if any, to, but excluding, the redemption date, equal to the greater of: (a) 100% of the aggregate principal amount of the 2.25% senior fixed-rate notes being redeemed on that redemption date; and (b) the sum of the present values of the remaining scheduled payments of principal and interest on the 2.25% senior fixed-rate notes being redeemed that would be due if the 2.25% senior fixed-rate notes to be redeemed matured on the Applicable Par Call Date (not including any portion of such payments of interest accrued to the redemption date) discounted to the redemption date on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the applicable Treasury Rate plus the Applicable Spread for the Notes to be redeemed. Additionally, on or after January 4, 2027, the 2.25% senior fixed-rate notes will also be redeemable, in whole or in part, at any time and from time to time, at the Bank’s option at a redemption price equal to 100% of the aggregate principal amount of the 2.25% senior fixed-rate notes being redeemed, plus accrued and unpaid interest thereon, if any, to, but excluding, the redemption date.
Fixed Rate 1.80 Percent Senior Notes Due 2023
Subsequent Event [Line Items]
Face amount of notes issued or redeemed		$ 650
Maturity date(s) End		Jan. 30, 2023
Debt Instrument, Redemption, Description		On or after the date that is 30 days before the maturity date, the 1.80% senior fixed-rate notes will be redeemable, in whole or in part, at any time and from time to time, at the Bank’s option at a redemption price equal to 100% of the aggregate principal amount of the 1.80% senior fixed-rate notes being redeemed, plus accrued and unpaid interest thereon, if any, to, but excluding, the redemption date.
Fixed Rate 2.25 Percent Notes Due 2027
Subsequent Event [Line Items]
Face amount of notes issued or redeemed		$ 600
Maturity date(s) Start		Jan. 31, 2020
Maturity date(s) End		Feb. 01, 2027
Aggregate Principal
Subsequent Event [Line Items]
Face amount of notes issued or redeemed		$ 1,250
Subsequent Event [Member] | Fixed Rate 2.25 Percent Notes Due 2027
Subsequent Event [Line Items]
Redemption Date Start	Jul. 31, 2020
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed	100.00%