Goodwill - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Business Acquisition [Line Items]
Goodwill (Note 3)	$ 1,244,000,000	$ 1,240,000,000	$ 1,108,000,000
Ally Financial International Operations [Member]
Business Acquisition [Line Items]
Aggregate consideration	3,300,000,000	3,300,000,000
Goodwill (Note 3)	138,000,000	138,000,000
North America Segment [Member]
Business Acquisition [Line Items]
Goodwill (Note 3)	$ 1,106,000,000	$ 1,108,000,000	$ 1,108,000,000	$ 1,108,000,000