Description of Business Description of Business - Cash and Available Revolver Capacity (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 1,454	$ 1,513
CERP
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	224
Revolver capacity	270
Revolver capacity drawn or committed to letters of credit	0
Total	494
CGP
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	1,031
Revolver capacity	160
Revolver capacity drawn or committed to letters of credit	0
Total	1,191
CES
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	84
Revolver capacity	0
Revolver capacity drawn or committed to letters of credit	0
Total	84
Other
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	115
Revolver capacity	0
Revolver capacity drawn or committed to letters of credit	0
Total	$ 115