Segment Information (Geographic Areas) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Deferred tax assets for long-lived assets	$ 129				$ 33				$ 129	$ 33
Revenues	3,727	3,877	3,711	3,596	3,738	3,820	3,868	3,837	14,911	15,263	15,215
Long-lived Assets	7,365				8,154				7,365	8,154
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									5,567	5,146	5,465
Long-lived Assets	2,114				2,212				2,114	2,212
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									1,285	1,244	1,359
Long-lived Assets	264				431				264	431
Mexico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									479	959	1,274
Long-lived Assets	170				226				170	226
Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									7,580	7,914	7,117
Long-lived Assets	$ 4,817				$ 5,285				$ 4,817	$ 5,285