Customer Financing (Financing Receivable Credit Quality Indicators) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 2,470	$ 2,442
Internally Assigned Grade [Member] | BBB Credit Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables by internal credit rating	1,165	1,201
Internally Assigned Grade [Member] | BB Credit Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables by internal credit rating	55	63
Internally Assigned Grade [Member] | B Credit Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables by internal credit rating	152	51
Internally Assigned Grade [Member] | CCC Credit Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables by internal credit rating	502	511
Internally Assigned Grade [Member] | D Credit Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables by internal credit rating	504	524
Internally Assigned Grade [Member] | Other Credit Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivables by internal credit rating	$ 92	$ 92