Debt - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)	Feb. 07, 2017 USD ($)	Nov. 30, 2016 EUR (€)	May 31, 2016 EUR (€)	Dec. 31, 2015 USD ($)
Maximum [Member]
Debt Instrument [Line Items]
Expiration period	24 months
Revolving Credit Facilities [Member] | Maximum [Member]
Debt Instrument [Line Items]
Expiration period	6 years
Senior Notes [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	3.33%
Face amount of debt	$ 29,008,000,000
Medium-term Notes [Member] | Euro Medium Term Note Due May 2020 [Member]
Debt Instrument [Line Items]
Face amount of debt | €				€ 500,000,000
Interest rate (percent)				1.168%
Medium-term Notes [Member] | Floating Rate Euro Medium Term Note Due December 2017 [Member]
Debt Instrument [Line Items]
Face amount of debt | €			€ 100,000,000
Line of Credit [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	7.50%
Debt instrument term	5 years
Line of Credit [Member] | Revolving Credit Facilities [Member]
Debt Instrument [Line Items]
Increase in unsecured committed credit facilities	$ 4,000,000,000
Unsecured Debt [Member]
Debt Instrument [Line Items]
Issuance costs	$ 115,000,000				$ 107,000,000
Secured Debt [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	2.09%
Issuance costs	$ 89,000,000				$ 76,000,000
Secured Debt [Member] | Securitization Notes Payable [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	1.70%
Face amount of debt	$ 16,909,000,000
International [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Increase in unsecured committed credit facilities	22,000,000
Parent Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Face amount of debt	$ 10,300,000,000.0
Parent Company [Member] | Senior Notes [Member] | Fixed Rate Senior Notes [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	3.38%
Face amount of debt	$ 9,600,000,000.0
Parent Company [Member] | Senior Notes [Member] | Floating Rate Senior Notes [Member]
Debt Instrument [Line Items]
Face amount of debt	$ 650,000,000
Subsequent Event [Member] | Parent Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Face amount of debt		$ 2,500,000,000.0
Interest rate (percent)		3.45%
Subsequent Event [Member] | Parent Company [Member] | Senior Notes [Member] | 4.35% Senior Notes Due January 2027 [Member]
Debt Instrument [Line Items]
Face amount of debt		$ 750,000,000
Interest rate (percent)		4.35%
Subsequent Event [Member] | Parent Company [Member] | Senior Notes [Member] | 3.45% Senior Notes Due January 2022 [Member]
Debt Instrument [Line Items]
Face amount of debt		$ 1,250,000,000.00
Subsequent Event [Member] | Parent Company [Member] | Senior Notes [Member] | Floating Rate Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Face amount of debt		$ 500,000,000