Correction of Errors in Previously Reported Consolidated Financial Statements (CompInc) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Correction of Previously Reported Financial Statements
Net income (loss)	$ 257	$ 236	$ 93	$ 241	$ 622	$ 395	$ 341	$ (461)	$ 827	$ 897	$ (1,900)
Net income (loss) attributable to noncontrolling interest									49	32	(61)
Net income (loss) attributable to controlling interest	$ 243	218	82	235	616	386	335	(472)	778	865	(1,839)
Components of net periodic benefit costs before reclassifications									(20)	63	(170)
Components of net periodic benefit costs reclassified to net income									8	23	17
Gain on derivative instruments reclassified to net income											(2)
Other comprehensive income (loss) before income taxes									(12)	86	(155)
Income taxes related to other comprehensive income									6	(17)	35
Other comprehensive income (loss)									(6)	69	(120)
Other comprehensive income attributable to controlling interest									(6)	69	(120)
Total comprehensive income (loss)									821	966	(2,020)
Total comprehensive income (loss) attributable to noncontrolling interest									49	32	(61)
Total comprehensive income attributable to controlling interest									$ 772	934	(1,959)
Previously reported
Correction of Previously Reported Financial Statements
Net income (loss)		244	88	255	617	330	348	(469)		826	(1,966)
Net income (loss) attributable to noncontrolling interest										35	(53)
Net income (loss) attributable to controlling interest		229	77	249	611	321	342	(483)		791	(1,913)
Components of net periodic benefit costs before reclassifications										63	(170)
Components of net periodic benefit costs reclassified to net income										23	17
Gain on derivative instruments reclassified to net income											(2)
Other comprehensive income (loss) before income taxes										86	(155)
Income taxes related to other comprehensive income										(16)	13
Other comprehensive income (loss)										70	(142)
Other comprehensive income attributable to controlling interest										70	(142)
Total comprehensive income (loss)										896	(2,108)
Total comprehensive income (loss) attributable to noncontrolling interest										35	(53)
Total comprehensive income attributable to controlling interest										861	(2,055)
Adjusted
Correction of Previously Reported Financial Statements
Net income (loss)		(8)	5	(14)	5	65	(7)	8		71	66
Net income (loss) attributable to noncontrolling interest										(3)	(8)
Net income (loss) attributable to controlling interest		$ (11)	$ 5	$ (14)	$ 5	$ 65	$ (7)	$ 11		74	74
Income taxes related to other comprehensive income										(1)	22
Other comprehensive income (loss)										(1)	22
Other comprehensive income attributable to controlling interest										(1)	22
Total comprehensive income (loss)										70	88
Total comprehensive income (loss) attributable to noncontrolling interest										(3)	(8)
Total comprehensive income attributable to controlling interest										$ 73	$ 96