Acquisitions and Disposals - Transaction Related Costs - Catlin (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Costs incurred in 2015	$ 156,368
2015 payments	99,079
Liabilities at December 31, 2015	57,289
Severance related costs
Business Acquisition [Line Items]
Costs incurred in 2015	47,185
2015 payments	31,058
Liabilities at December 31, 2015	16,127
Retention and other compensation costs
Business Acquisition [Line Items]
Costs incurred in 2015	35,310
2015 payments	18,341
Liabilities at December 31, 2015	16,969
Facilities-related costs
Business Acquisition [Line Items]
Costs incurred in 2015	14,744
2015 payments	13,926
Liabilities at December 31, 2015	818
Consulting and other
Business Acquisition [Line Items]
Costs incurred in 2015	59,129
2015 payments	35,754
Liabilities at December 31, 2015	$ 23,375