Commitments and Contingencies - Legal Narrative (Details) € in Millions, £ in Millions, NZD in Millions											1 Months Ended				3 Months Ended		12 Months Ended
	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 29, 2015 NZD	Jan. 26, 2015 USD ($)	Jan. 26, 2015 CHF (SFr)	Dec. 02, 2014 USD ($)	Dec. 02, 2014 CHF (SFr)	Jan. 02, 2014 GBP (£)	Jun. 01, 2007 USD ($)	Jun. 01, 2007 CHF (SFr)	Aug. 31, 2015 USD ($)	Jun. 30, 2015 GBP (£)	Mar. 31, 2015 USD ($)	May. 31, 2010 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2015 EUR (€)	Dec. 31, 2015 USD ($)	Apr. 30, 2014 GBP (£)
Loss Contingencies [Line Items]
Range of possible loss, minimum	$ 0																$ 0
Range of possible loss, maximum	300,000,000																300,000,000
Potential Claim for Pension Advisory Services [Member]
Loss Contingencies [Line Items]
Estimate of possible loss	67,000,000																67,000,000	£ 45
Opry Mills Mall Limited Partnership [Member]
Loss Contingencies [Line Items]
Value of damages sought														$ 200,000,000
Amount of coverage for damages contended by the insurers														50,000,000
Difference amount of damages sought by the client														$ 150,000,000
Opry Mills Mall Limited Partnership [Member]
Loss Contingencies [Line Items]
Damages awarded											$ 204,000,000		$ 200,000,000
International Road Transport Union [Member] | Litigation Foreign Currency Denominated Award [Member]
Loss Contingencies [Line Items]
Value of damages sought										SFr 46,000,000							47,000,000
Damages awarded excluding interest and costs						$ 17,000,000	SFr 16,800,000
Damages awarded						28,000,000	SFr 27,900,000
Litigation settlement				$ 13,000,000	SFr 12,800,000
Settlement agreement terms maximum liability				9,000,000	SFr 8,700,000.0
International Road Transport Union [Member] | Litigation USD Denominated Award [Member]
Loss Contingencies [Line Items]
Value of damages sought									$ 3,000,000
Damages awarded excluding interest and costs						3,100,000
Damages awarded						$ 5,000,000
Litigation settlement				4,700,000
Settlement agreement terms maximum liability				$ 115,000
International Road Transport Union [Member] | Litigation Expenses and Interest [Member]
Loss Contingencies [Line Items]
Value of damages sought									$ 30,000,000
Philips [Member]
Loss Contingencies [Line Items]
Value of damages sought	432,000,000							£ 189				£ 290					$ 282,000,000
Versicherung Aktiengesellschaft [Member] | Litigation Foreign Currency Denominated Award [Member]
Loss Contingencies [Line Items]
Litigation settlement		$ (2,000,000)														€ (1.6)
Huntington Ingalls Industries [Member]
Loss Contingencies [Line Items]
Legal settlements															$ 150,000,000
Pending Litigation [Member] | Lyttleton Port Company Limited [Member]
Loss Contingencies [Line Items]
Value of damages sought	$ 125,900,000		NZD 184