Acquisitions and Exit Activities (Schedule of Purchase Price Allocation) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2015
Assets
Goodwill	$ 2,293	$ 2,286		$ 2,018
Gas Storage and Pipelines Acquisition
Assets
Cash			$ 83
Accounts receivable			24
Inventory			6
Property, plant, and equipment, net			719
Goodwill			275
Other current assets			1
Total assets			1,878
Liabilities
Accounts payable			19
Other current liabilities			11
Long-term debt			204
Other long-term liabilities			20
Total liabilities			254
Less: Noncontrolling interest			392
Total cash consideration			$ 1,232