Financial Instruments (Notational Amounts of Derivatives Held) (Details) $ in Millions	Mar. 31, 2021 USD ($)
Foreign exchange contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, notional amount	$ 1,711
Interest rate caps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, notional amount	8,686
Interest rate caps | Subsidiaries
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, notional amount	3,000
Interest rate swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, notional amount	1,950
Sold
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, notional amount	5,800
Purchase
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, notional amount	$ 2,800