Long-Term Debt (Long-Term Debt - Additional Information) (Detail) - Bank Notes Program - USD ($) $ in Millions		3 Months Ended
	Jan. 31, 2020	Mar. 31, 2020
Debt Instrument
Debt Instrument, Face Amount	$ 1,250
1.80% Senior fixed-rate notes
Debt Instrument
Debt Instrument, Face Amount	$ 650
Long-term debt, interest rate	1.80%
Long-term debt, maturity term	3 years
Long-term debt, maturity date	Jan. 30, 2023
Long-term debt, redemption terms		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.
Long-term debt, redemption price percentage		100.00%
2.25% Senior fixed-rate notes
Debt Instrument
Debt Instrument, Face Amount	$ 600
Long-term debt, interest rate	2.25%
Long-term debt, maturity term	7 years
Long-term debt, maturity date	Feb. 01, 2027
Long-term debt, redemption terms		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.
Long-term debt, redemption price percentage		100.00%