Goodwill, Other Intangibles, and Property and Equipment - Useful Life (Details)	12 Months Ended
	Dec. 31, 2017
Building improvements [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment useful life	10 years
Building improvements [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment useful life	40 years
Purchased software [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment useful life	3 years
Purchased software [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment useful life	5 years
Internally developed software [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment useful life	3 years
Internally developed software [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment useful life	7 years
Furniture and equipment (including computer equipment) [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment useful life	3 years
Furniture and equipment (including computer equipment) [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment useful life	10 years