Segment Reporting Segment Reporting - Condensed Balance Sheets - By Segment (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 14,812	$ 14,894
Total liabilities	16,738	16,312
Operating Segments [Member] | CERP
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	6,959	6,941
Total liabilities	5,876	5,903
Operating Segments [Member] | CGP
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	7,290	7,353
Total liabilities	2,664	2,709
Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	1,217	1,246
Total liabilities	8,263	7,758
Eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	(654)	(646)
Total liabilities	$ (65)	$ (58)