Retirement Plans and Postretirement Medical Benefits (Fair Value Measurements of Plan Assets) (Details) (USD $) | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 |
In Thousands, unless otherwise specified |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | $1,114,543 | | $1,024,033 | | | |
Cash | 1,079,145 | | 907,806 | | 913,276 | 856,238 |
Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 619,617 | | 526,489 | | | |
Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 494,926 | | 497,544 | | | |
Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 1,719,936 | | 1,524,759 | | | |
Securities lending payable | -131,901 | [1] | -6,602 | [1] | | |
Cash | 4,621 | | 634 | | | |
Other | 807 | | 4,888 | | | |
Fair value of plan assets available for benefits | 1,593,463 | | 1,523,679 | | 1,583,932 | |
United States | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 364,278 | | 323,378 | | | |
United States | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 1,197,563 | | 1,043,360 | | | |
United States | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 158,095 | | 158,021 | | | |
United States | Money market funds | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 10,758 | | 30,374 | | | |
United States | Money market funds | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Money market funds | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 10,758 | | 30,374 | | | |
United States | Money market funds | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Equity securities | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 326,785 | | 445,291 | | | |
United States | Equity securities | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 180,069 | | 279,988 | | | |
United States | Equity securities | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 146,716 | | 165,303 | | | |
United States | Equity securities | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Commingled fixed income securities | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 261,571 | | 209,674 | | | |
United States | Commingled fixed income securities | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Commingled fixed income securities | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 261,571 | | 209,674 | | | |
United States | Commingled fixed income securities | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Debt securities - U.S. and foreign governments, agencies and municipalities | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 209,340 | | 73,867 | | | |
United States | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 184,209 | | 43,390 | | | |
United States | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 25,131 | | 30,477 | | | |
United States | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Debt securities - corporate | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 598,927 | | 568,567 | | | |
United States | Debt securities - corporate | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Debt securities - corporate | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 598,927 | | 568,567 | | | |
United States | Debt securities - corporate | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Mortgage-backed securities | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 22,503 | | 34,372 | | | |
United States | Mortgage-backed securities | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Mortgage-backed securities | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 20,401 | | 31,738 | | | |
United States | Mortgage-backed securities | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 2,102 | | 2,634 | | | |
United States | Asset-backed securities | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 2,158 | | 625 | | | |
United States | Asset-backed securities | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Asset-backed securities | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 2,158 | | 625 | | | |
United States | Asset-backed securities | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Private equity | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 81,246 | | 87,470 | | | |
United States | Private equity | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Private equity | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Private equity | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 81,246 | | 87,470 | | | |
United States | Real estate | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 74,747 | | 67,917 | | | |
United States | Real estate | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Real estate | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
United States | Real estate | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 74,747 | | 67,917 | | | |
United States | Securities lending collateral | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 131,901 | [1] | 6,602 | [1] | | |
United States | Securities lending collateral | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | [1] | 0 | [1] | | |
United States | Securities lending collateral | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 131,901 | [1] | 6,602 | [1] | | |
United States | Securities lending collateral | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | [1] | 0 | [1] | | |
Foreign | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 560,060 | | 554,725 | | | |
Cash | 10,859 | | 5,285 | | | |
Other | 4,073 | | 1,068 | | | |
Fair value of plan assets available for benefits | 574,992 | | 561,078 | | 509,331 | |
Foreign | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 99,570 | | 109,403 | | | |
Foreign | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 460,490 | | 445,322 | | | |
Foreign | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
Foreign | Money market funds | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 6,684 | | 6,058 | | | |
Foreign | Money market funds | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
Foreign | Money market funds | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 6,684 | | 6,058 | | | |
Foreign | Money market funds | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
Foreign | Equity securities | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 290,494 | | 366,449 | | | |
Foreign | Equity securities | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 99,570 | | 109,403 | | | |
Foreign | Equity securities | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 190,924 | | 257,046 | | | |
Foreign | Equity securities | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
Foreign | Commingled fixed income securities | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 151,017 | | 104,070 | | | |
Foreign | Commingled fixed income securities | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
Foreign | Commingled fixed income securities | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 151,017 | | 104,070 | | | |
Foreign | Commingled fixed income securities | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
Foreign | Debt securities - U.S. and foreign governments, agencies and municipalities | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 85,711 | | 60,204 | | | |
Foreign | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
Foreign | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 85,711 | | 60,204 | | | |
Foreign | Debt securities - U.S. and foreign governments, agencies and municipalities | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
Foreign | Debt securities - corporate | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 26,154 | | 17,944 | | | |
Foreign | Debt securities - corporate | Level 1 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 0 | | 0 | | | |
Foreign | Debt securities - corporate | Level 2 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | 26,154 | | 17,944 | | | |
Foreign | Debt securities - corporate | Level 3 | | | | | | |
Defined Benefit Plan Disclosure [Line Items] | | | | | | |
Total plan assets at fair value | $0 | | $0 | | | |
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[1] | Securities lending collateral is offset by a corresponding securities lending payable amount. |