Benefit Plans (Summary of the Components of Net Periodic Benefit Cost Recognized for Pension Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 176	$ 138	$ 150
Interest cost	157	140	120
Estimated return on plan assets	(327)	(296)	(257)
Net amortization and other	67	17	91
Net periodic benefit cost	73	(1)	104
Net actuarial loss (gain)	230	532	(535)
Net amortization	(67)	(17)	(91)
Net amount recognized in OCI	163	515	(626)
Total net periodic pension costs (income) recognized in total comprehensive income, pre-tax	$ 236	$ 514	$ (522)