Postretirement Benefits (Details 7) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Amounts included in shareholders' equity (unamortized):
Net actuarial loss	$ 220	$ 173
Prior service cost	6	6
Net amount not yet recognized	226	179
Amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost during next fiscal year
Estimated net actuarial loss recognized in net periodic benefit cost before tax	15
Estimated net prior service cost recognized in net periodic benefit cost before tax	$ 1