Basis of Presentation and Summary of Significant Accounting Policies (Details 1) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in accounting estimates
Net income	$ 1,117	$ 92	$ 17	$ 163	$ 42	$ 152	$ 196	$ 236	$ 1,389	$ 626	$ 878
Change in accounting method accounted for as a change in estimate
Change in accounting estimates
Combined decrease in pension and post-retirement cost									(122)	(149)
Net income									$ 75	$ 91
Earnings per share, basic and diluted									$ 0.12	$ 0.17