Borrowings and Capital Leases (Senior Notes Issued by SAIIDAC) (Details) - SAIIDAC notes - Senior Notes - USD ($)	Mar. 31, 2018	Sep. 23, 2016
Debt Instrument [Line Items]
Aggregate amount	$ 12,100,000,000
Carrying amount	12,053,300,000
Fixed-rate notes due 2019
Debt Instrument [Line Items]
Aggregate amount	$ 3,300,000,000
Coupon rate	1.90%	1.90%
Carrying amount	$ 3,293,100,000
Fixed-rate notes due 2021
Debt Instrument [Line Items]
Aggregate amount	$ 3,300,000,000
Coupon rate	2.40%	2.40%
Carrying amount	$ 3,287,200,000
Fixed-rate notes due 2023
Debt Instrument [Line Items]
Aggregate amount	$ 2,500,000,000
Coupon rate	2.875%	2.875%
Carrying amount	$ 2,490,000,000
Fixed-rate notes due 2026
Debt Instrument [Line Items]
Aggregate amount	$ 3,000,000,000
Coupon rate	3.20%	3.20%
Carrying amount	$ 2,983,000,000