Summary of Significant Accounting Policies - Goodwill Impairment Test (Details)	12 Months Ended
	Dec. 31, 2014
Market Approach Assumption [Member]
Goodwill Impairment Test [Line Items]
Trailing-twelve months earnings multiple	9.4
Forward earnings multiple	8.9
Weighting applied (percent)	25.00%
Income Approach Assumption [Member]
Goodwill Impairment Test [Line Items]
Weighting applied (percent)	75.00%
Cost of equity (percent)	9.20%
Income Approach Assumption [Member] | Maximum [Member]
Goodwill Impairment Test [Line Items]
Targeted equity-to-earning assets ratio	10.50%
Income Approach Assumption [Member] | Minimum [Member]
Goodwill Impairment Test [Line Items]
Targeted equity-to-earning assets ratio	7.50%
North America Segment [Member]
Goodwill Impairment Test [Line Items]
Fair value in excess of carrying amount (percent)	59.00%
North America Segment [Member] | Goodwill [Member]
Goodwill Impairment Test [Line Items]
Percentage of goodwill balance	89.00%