Retirement Plans and Postretirement Medical Benefits (Level 3 Gains and Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
United States
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	$ 147,738	$ 158,095
Realized gains	11,488	15,325
Unrealized gains	(2,687)	227
Net purchases, sales and settlements	(17,814)	(25,909)
Balance at	138,725	147,738
United States | Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	1,592	2,102
Realized gains	8	10
Unrealized gains	38	28
Net purchases, sales and settlements	(402)	(548)
Balance at	1,236	1,592
United States | Private equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	63,577	81,246
Realized gains	10,200	14,288
Unrealized gains	(7,540)	(6,844)
Net purchases, sales and settlements	(16,600)	(25,113)
Balance at	49,637	63,577
United States | Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	82,569	74,747
Realized gains	1,280	1,027
Unrealized gains	4,815	7,043
Net purchases, sales and settlements	(812)	(248)
Balance at	87,852	82,569
Foreign
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	59,690	0
Unrealized gains	3,020	(1,804)
Net purchases, sales and settlements	20,464	61,494
Foreign currency gain/(loss)	(11,912)
Balance at	71,262	59,690
Foreign | Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	39,177	0
Unrealized gains	459	(1,685)
Net purchases, sales and settlements	1,436	40,862
Foreign currency gain/(loss)	(6,589)
Balance at	34,483	39,177
Foreign | Diversified growth funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	20,513	0
Unrealized gains	2,561	(119)
Net purchases, sales and settlements	19,028	20,632
Foreign currency gain/(loss)	(5,323)
Balance at	$ 36,779	$ 20,513