Investments In and Advances To Affiliates - Summarized Financial Information (Details) - USD ($) $ in Millions			3 Months Ended								12 Months Ended
	Nov. 15, 2017	Jul. 25, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Schedule of Equity Method Investments [Line Items]
Revenue			$ 2,622	$ 2,837	$ 2,537	$ 2,740	$ 2,643	$ 2,693	$ 2,613	$ 2,581	$ 10,736	$ 10,530	$ 10,281
Operating margin			646	671	600	656	645	640	623	557	2,573	2,465	2,383
Net income (loss)			181	$ 191	$ 416	$ 777	(1,286)	$ 261	$ 150	$ 98	1,565	(777)	(777)
Assets, Current			5,015				6,398				5,015	6,398
Liabilities, Current			4,399				6,028				4,399	6,028
Liabilities, Noncurrent			21,639				21,402				21,639	21,402
Stockholders' Equity Attributable to Noncontrolling Interest			2,396				2,380				2,396	2,380		$ 2,461
Stockholders' Equity Attributable to Parent			3,208				2,465				3,208	2,465
Undistributed Earnings Of Minority Owned Affiliates Included In Retained Earnings			236								236
Distributions Received From Minority Owned Affiliates											42	69	24
Basis Difference Between Carrying Amount And Investment			49								49
Minority Owned Affiliates
Schedule of Equity Method Investments [Line Items]
Revenue											962	762	586
Operating margin											135	165	145
Net income (loss)											14	72	64
Assets, Current			558				418				558	418
Assets, Noncurrent			5,918				5,372				5,918	5,372
Liabilities, Current			546				633				546	633
Liabilities, Noncurrent			3,309				2,629				3,309	2,629
Stockholders' Equity Attributable to Parent			2,622				2,527				2,622	2,527
Majority Owned Affiliates
Schedule of Equity Method Investments [Line Items]
Revenue											40	16	23
Operating margin											3	5	9
Net income (loss)											(3)	(15)	$ (2)
Assets, Current			89				70				89	70
Assets, Noncurrent			41				102				41	102
Liabilities, Current			35				10				35	10
Liabilities, Noncurrent			122				147				122	147
Stockholders' Equity Attributable to Parent			$ (27)				$ 15				$ (27)	$ 15
sPower [Member]
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	$ 19	$ 461