Benefit Plans - Fair Value (Details) (USD $) In Millions, unless otherwise specified																																																					12 Months Ended
	Dec. 31, 2011 Pension Benefits	Dec. 31, 2010 Pension Benefits	Dec. 31, 2009 Pension Benefits	Dec. 31, 2011 Pension Benefits Cash and cash equivalents	Dec. 31, 2010 Pension Benefits Cash and cash equivalents	Dec. 31, 2011 Pension Benefits International equity securities	Dec. 31, 2010 Pension Benefits International equity securities	Dec. 31, 2011 Pension Benefits Domestic equity securities	Dec. 31, 2010 Pension Benefits Domestic equity securities	Dec. 31, 2011 Pension Benefits Private equity securities	Dec. 31, 2010 Pension Benefits Private equity securities	Dec. 31, 2011 Pension Benefits Corporate bonds	Dec. 31, 2010 Pension Benefits Corporate bonds	Dec. 31, 2011 Pension Benefits U.S. state and municipal debt	Dec. 31, 2010 Pension Benefits U.S. state and municipal debt	Dec. 31, 2011 Pension Benefits U.S. and foreign government debt	Dec. 31, 2010 Pension Benefits U.S. and foreign government debt	Dec. 31, 2011 Pension Benefits Commingled funds	Dec. 31, 2010 Pension Benefits Commingled funds	Dec. 31, 2011 Pension Benefits Hedge funds	Dec. 31, 2010 Pension Benefits Hedge funds	Dec. 31, 2011 Pension Benefits Timber investments	Dec. 31, 2010 Pension Benefits Timber investments	Dec. 31, 2011 Pension Benefits Other investments	Dec. 31, 2010 Pension Benefits Other investments	Dec. 31, 2011 Pension Benefits Level 1	Dec. 31, 2010 Pension Benefits Level 1	Dec. 31, 2011 Pension Benefits Level 1 Cash and cash equivalents	Dec. 31, 2010 Pension Benefits Level 1 Cash and cash equivalents	Dec. 31, 2011 Pension Benefits Level 1 International equity securities	Dec. 31, 2010 Pension Benefits Level 1 International equity securities	Dec. 31, 2011 Pension Benefits Level 1 Domestic equity securities	Dec. 31, 2010 Pension Benefits Level 1 Domestic equity securities	Dec. 31, 2011 Pension Benefits Level 1 U.S. and foreign government debt	Dec. 31, 2010 Pension Benefits Level 1 U.S. and foreign government debt	Dec. 31, 2011 Pension Benefits Level 2	Dec. 31, 2010 Pension Benefits Level 2	Dec. 31, 2011 Pension Benefits Level 2 Cash and cash equivalents	Dec. 31, 2010 Pension Benefits Level 2 Cash and cash equivalents	Dec. 31, 2010 Pension Benefits Level 2 Domestic equity securities	Dec. 31, 2011 Pension Benefits Level 2 Corporate bonds	Dec. 31, 2010 Pension Benefits Level 2 Corporate bonds	Dec. 31, 2011 Pension Benefits Level 2 U.S. state and municipal debt	Dec. 31, 2010 Pension Benefits Level 2 U.S. state and municipal debt	Dec. 31, 2011 Pension Benefits Level 2 U.S. and foreign government debt	Dec. 31, 2010 Pension Benefits Level 2 U.S. and foreign government debt	Dec. 31, 2011 Pension Benefits Level 2 Commingled funds	Dec. 31, 2010 Pension Benefits Level 2 Commingled funds	Dec. 31, 2011 Pension Benefits Level 2 Hedge funds	Dec. 31, 2010 Pension Benefits Level 2 Hedge funds	Dec. 31, 2011 Pension Benefits Level 2 Other investments	Dec. 31, 2010 Pension Benefits Level 2 Other investments	Dec. 31, 2011 Pension Benefits Level 3	Dec. 31, 2010 Pension Benefits Level 3	Dec. 31, 2011 Pension Benefits Level 3 Private equity securities	Dec. 31, 2010 Pension Benefits Level 3 Private equity securities	Dec. 31, 2011 Pension Benefits Level 3 Hedge funds	Dec. 31, 2010 Pension Benefits Level 3 Hedge funds	Dec. 31, 2011 Pension Benefits Level 3 Timber investments	Dec. 31, 2010 Pension Benefits Level 3 Timber investments	Dec. 31, 2011 Other Postretirement Benefits	Dec. 31, 2010 Other Postretirement Benefits	Dec. 31, 2009 Other Postretirement Benefits
Fair Value Hierarchy Of Pension Plan Assets [Line Items]
Total assets				$ 115	$ 94	$ 47	$ 40	$ 266	$ 286	$ 153	$ 147	$ 407	$ 216	$ 42	$ 19	$ 349	$ 174	$ 490	$ 847	$ 306	$ 53	$ 11	$ 11	$ 5	$ 4			$ 82	$ 0	$ 47	$ 40	$ 266	$ 286	$ 247	$ 144			$ 33	$ 94	$ 0	$ 407	$ 216	$ 42	$ 19	$ 102	$ 30	$ 490	$ 847	$ 159	$ 51	$ 5	$ 4			$ 153	$ 147	$ 147	$ 2	$ 11	$ 11
Fair value of plan assets	2,191	1,891	1,673																							642	470									1,238	1,261																311	160							37	33	55
Defined benefit plan changes in level 3
Balance at January 1																																																					160	138	147	122	2	2	11	14
Net realized and unrealized gains (losses)																																																					5	5	0	7	4	0	1	(2)
Transfers in																																																					52				52
Purchases, sales and distributions, net																																																					94	17	6	18	89	0	(1)	(1)
Balance at December 31																																																					$ 311	$ 160	$ 153	$ 147	$ 147	$ 2	$ 11	$ 11