SCHEDULE I, CONDENSED FINANCIAL INFORMATION OF PARENT - BALANCE SHEETS (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Assets [Abstract]
Cash and cash equivalents	$ 288	$ 349	[1]
Due from affiliates	37	26	[1]
Income taxes receivable	110	43	[1]
Other current assets	136	142	[1]
Total current assets	3,341	3,110	[1]
Investments in subsidiaries	2,527	2,097	[1]
Due from affiliates	598	201	[1]
Deferred income taxes	170	234	[1]
Other assets	792	520	[1]
Total assets	50,454	47,786	[1]	$ 41,150
Liabilities and shareholders’ equity:
Current portion of long-term debt	1,427	913	[1]
Due to affiliates	7	11	[1]
Other current liabilities	545	517	[1]
Total current liabilities	6,635	5,927	[1]
Long-term debt	16,445	14,429	[1]
Due to affiliates	35	0	[1]
Shareholders’ equity	12,670	12,951	[1]
Total liabilities and equity	50,454	47,786	[1]
Parent Company [Member]
Assets [Abstract]
Cash and cash equivalents	104	12		$ 4	$ 3
Due from affiliates	83	73
Income taxes receivable	272	0
Other current assets	6	2
Total current assets	465	87
Investments in subsidiaries	17,924	17,329
Due from affiliates	2	0
Deferred income taxes	1,802	2,570
Other assets	656	592
Total assets	20,849	20,578
Liabilities and shareholders’ equity:
Current portion of long-term debt	500	600
Due to affiliates	280	359
Income taxes payable	0	153
Other current liabilities	396	374
Total current liabilities	1,176	1,486
Long-term debt	6,198	5,100
Due to affiliates	300	517
Other long-term liabilities	505	524
Shareholders’ equity	12,670	12,951
Total liabilities and equity	$ 20,849	$ 20,578

[1] Reflects reclassifications to conform to current year presentation, which we discuss in Note 1.