Debt - Narrative (Details)	9 Months Ended	12 Months Ended				12 Months Ended					1 Months Ended			12 Months Ended			12 Months Ended		12 Months Ended				1 Months Ended					1 Months Ended											12 Months Ended
	Sep. 30, 2014 CAD	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2014 Secured Debt [Member] USD ($)	Dec. 31, 2013 Secured Debt [Member] USD ($)	Dec. 31, 2014 Securitization Notes Payable [Member] USD ($)	Dec. 31, 2013 Securitization Notes Payable [Member] USD ($)	Dec. 31, 2012 Securitization Notes Payable [Member] USD ($)	Dec. 31, 2014 Unsecured Debt [Member] USD ($)	Dec. 31, 2013 Unsecured Debt [Member] USD ($)	Oct. 31, 2014 European Medium Term Notes [Member] EUR (€)	Dec. 31, 2014 North America [Member] USD ($)	Dec. 31, 2013 North America [Member] USD ($)	Dec. 31, 2014 North America [Member] Secured Debt [Member]	Dec. 31, 2014 North America [Member] Senior Notes [Member]	Sep. 30, 2014 North America [Member] Senior Notes [Member] USD ($)	Dec. 31, 2014 International [Member] USD ($)	Dec. 31, 2013 International [Member] USD ($)	Dec. 31, 2014 International [Member] Revolving Credit Facilities [Member] USD ($)	Dec. 31, 2013 International [Member] Revolving Credit Facilities [Member] USD ($)	Dec. 31, 2014 International [Member] Unsecured Debt [Member]	Dec. 31, 2014 International [Member] Line of Credit [Member] USD ($)	Sep. 30, 2014 Parent Company [Member] USD ($)	Jul. 31, 2014 Parent Company [Member] USD ($)	Dec. 31, 2014 Parent Company [Member] USD ($)	Oct. 31, 2014 Parent Company [Member] USD ($)	Dec. 31, 2013 Parent Company [Member] USD ($)	Jul. 31, 2014 Parent Company [Member] July 2017 [Member] USD ($)	Jul. 31, 2014 Parent Company [Member] July 2019 [Member] USD ($)	Sep. 30, 2014 Parent Company [Member] September 2017 [Member] USD ($)	Sep. 30, 2014 Parent Company [Member] September 2021 [Member] USD ($)	Dec. 31, 2014 Parent Company [Member] Senior Notes [Member] USD ($)	Feb. 04, 2015 Parent Company [Member] Senior Notes [Member] Subsequent Event [Member] USD ($)	Feb. 04, 2015 Parent Company [Member] Senior Notes [Member] Senior Notes Due January 2020 [Member] Subsequent Event [Member] USD ($)	Feb. 04, 2015 Parent Company [Member] Senior Notes [Member] Senior Notes Due January 2025 [Member] Subsequent Event [Member] USD ($)	Feb. 04, 2015 Parent Company [Member] Senior Notes [Member] Floating Rate Senior Notes Due January 2020 [Member] London Interbank Offered Rate (LIBOR) [Member] Subsequent Event [Member] USD ($)	Dec. 31, 2014 Revolving Credit Facilities [Member] USD ($)	Dec. 31, 2013 Revolving Credit Facilities [Member] USD ($)	Dec. 31, 2014 Revolving Credit Facilities [Member] Maximum [Member]	Dec. 31, 2014 Revolving Credit Facilities [Member] North America [Member] USD ($)	Dec. 31, 2013 Revolving Credit Facilities [Member] North America [Member] USD ($)	Dec. 31, 2014 Revolving Credit Facilities [Member] International [Member] USD ($)	Dec. 31, 2013 Revolving Credit Facilities [Member] International [Member] USD ($)
Debt Instrument [Line Items]
Interest rate, minimum (percent)											1.875%			1.00%	1.875%		0.35%				0.98%		3.00%	2.625%
Interest rate, maximum (percent)														4.65%	6.75%		13.43%				13.35%		4.375%	3.50%
Issuance costs				$ 60,000,000	$ 37,000,000				$ 75,000,000	$ 40,000,000
Expiration period																																							5 years
Total borrowing capacity		5,500,000,000																				282,000,000	11,000,000,000.0			12,500,000,000.0
Secured debt		25,214,000,000	22,073,000,000			10,700,000,000						15,454,000,000	12,479,000,000				9,760,000,000	9,594,000,000							0		0										7,028,000,000	7,364,000,000		1,701,000,000	1,678,000,000	5,327,000,000	5,686,000,000
Weighted average interest rate (percent)						1.40%
Amortization of purchase accounting premium						1,000,000	10,000,000	32,000,000
Accretion of discount																			30,000,000	12,000,000
Unsecured debt		12,217,000,000	6,973,000,000									7,846,000,000	4,000,000,000			8,400,000,000	4,371,000,000	2,973,000,000							7,500,000,000		4,000,000,000					7,500,000,000					2,974,000,000	2,370,000,000		0	0	2,974,000,000	2,370,000,000
Acquisition accounting discount - secured debt																			17,000,000
Proceeds from issuance of medium-term notes											500,000,000
Proceeds from issuance of senior long-term debt	400,000,000																						2,000,000,000	1,500,000,000				700,000,000	800,000,000	750,000,000	1,250,000,000
Face amount of debt		8,400,000,000	4,000,000,000																														2,000,000,000.0	1,000,000,000.0	1,000,000,000.0	250,000,000
Interest rate (percent)	3.25%																																	3.15%	4.00%	1.56%
Accretion expense		4,000,000	2,000,000
Unamortized discount		$ 1,000,000