Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 779	$ 696	$ 1,447	$ 1,352
Net actuarial gains (losses) of defined benefit plans:
Adjustments	(18)	0	(30)	(10)
Recognized within Net income	13	17	27	27
Prior service (cost) credit of defined benefit plans:
Adjustments	1	0	1	0
Recognized within Net income	(1)	0	(2)	1
Other comprehensive income (loss)	(5)	17	(4)	18
Total comprehensive income	$ 774	$ 713	$ 1,443	$ 1,370

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount after tax of cost (credit) of benefit changes attributable to plan participants' prior service resulting from a plan amendment or plan initiation that has not been recognized in net periodic benefit cost (credit).

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Amount after tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit.

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