| Cost of Pension Plans | | | | | | | | | | | | | | | | | | | | | | | | | | |
| | Total | | Principal pension plans | | Other pension plans |
| (In millions) | | 2013 | | | 2012 | | | 2011 | | | 2013 | | | 2012 | | | 2011 | | | 2013 | | | 2012 | | | 2011 |
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| Service cost for benefits earned | $ | 1,970 | | $ | 1,779 | | $ | 1,498 | | $ | 1,535 | | $ | 1,387 | | $ | 1,195 | | $ | 435 | | $ | 392 | | $ | 303 |
| Prior service cost amortization | | 253 | | | 287 | | | 207 | | | 246 | | | 279 | | | 194 | | | 7 | | | 8 | | | 13 |
| Expected return on plan assets | | (4,163) | | | (4,394) | | | (4,543) | | | (3,500) | | | (3,768) | | | (3,940) | | | (663) | | | (626) | | | (603) |
| Interest cost on benefit obligations | | 2,983 | | | 2,993 | | | 3,176 | | | 2,460 | | | 2,479 | | | 2,662 | | | 523 | | | 514 | | | 514 |
| Net actuarial loss amortization | | 4,007 | | | 3,701 | | | 2,486 | | | 3,664 | | | 3,421 | | | 2,335 | | | 343 | | | 280 | | | 151 |
| Pension plans cost | $ | 5,050 | | $ | 4,366 | | $ | 2,824 | | $ | 4,405 | | $ | 3,798 | | $ | 2,446 | | $ | 645 | | $ | 568 | | $ | 378 |
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