Debt - Asset Financing (Details) - Unsecured Debt - Asset financing and other	12 Months Ended
	Dec. 31, 2018
Debt Instrument [Line Items]
Weighted average interest rate	1.47%
Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	0.53%
Term of debt instrument	5 years
Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	4.97%
Term of debt instrument	10 years