Long-Term Debt - Senior and Subordinated Debt (Details) - Subsidiaries - USD ($) $ in Millions				12 Months Ended
	Jan. 31, 2020	Jul. 26, 2018	Mar. 15, 2016	Dec. 31, 2024
Debt Instrument
Global Bank note program				$ 25,000
Debt, available for future issuance				$ 20,400
Subordinated Debt | Fixed Rate 3.85% Notes Due 2026
Debt Instrument
Principal amount			$ 750
Interest rate (as a percent)			3.85%	3.85%
Redemption period prior to maturity date			30 days
Redemption price (as a percent)			100.00%
Senior Notes | Fixed rate 395 percent notes due 2025 [Member]
Debt Instrument
Principal amount		$ 750
Interest rate (as a percent)		3.95%		3.95%
Redemption period prior to maturity date		30 days
Redemption price (as a percent)		100.00%
Derivative, basis spread on a variable rate				1.16%
Derivative, variable interest rate				5.70%
Senior Notes | Fixed Rate 2.25% Notes Due 2027
Debt Instrument
Principal amount	$ 600
Interest rate (as a percent)	2.25%			2.25%
Redemption price (as a percent)	100.00%
Minimum | Medium-Term Senior Notes and Subordinated Bank Notes
Debt Instrument
Debt term				1 year
Maximum | Medium-Term Senior Notes and Subordinated Bank Notes
Debt Instrument
Debt term				30 years