Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements of Comprehensive Income [Abstract]
Tax benefit of change in postretirement benefit plans	$ 399	$ (19)	$ (88)
Tax expense of net change in unrealized gains on investment securities	8	0	(7)
Tax (expense) benefit of prior service gain from plan amendment	(1)	1	(1)
Tax (expense) benefit of net actuarial gain (loss) arising during the period	356	14	(61)
Tax benefit of amortization of prior service costs (approx.)	(1)	(1)	(2)
Tax benefit of amortization of net actuarial loss	(42)	(33)	(24)
Tax benefit (expense) of unrealized holding (losses) gains arising during period	2	(3)	(7)
Tax expense of gains realized during the period	$ 6	$ 3	$ 0