Consolidated Statements of Changes in Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Long-term income tax receivable [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income, Net [Member]	Noncontrolling Interest [Member]
Balance (shares) at Dec. 31, 2016		77
Balance at Dec. 31, 2016	$ 24,463	$ 0	$ 6,390		$ 19,448	$ (1,511)	$ 136
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	1,139	0	0		1,130	0	9
Other comprehensive income (loss)	422	0	0		0	422	0
Common stock purchases	(19)	0	(1)		(18)	0	0
Conversion of Stock, Amount Converted	(100)		(6)		(94)
Distributions	(12)	0	0		0	0	(12)
Other equity transactions	(23)	$ 0	(21)		1	0	(3)
Balance (shares) at Jun. 30, 2017		77
Balance at Jun. 30, 2017	25,870	$ 0	6,362		20,467	(1,089)	130
Long-term income tax receivable	$ 0
Balance (shares) at Dec. 31, 2017	77	77
Balance at Dec. 31, 2017	$ 28,308	$ 0	6,368		22,206	(398)	132
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	0				1,085	(1,085)
Net Income	893	0	0		885	0	8
Other comprehensive income (loss)	(182)	0	0		0	(182)	0
Reclassification of long-term income tax receivable	(609)			$ (609)
Long-term income tax receivable adjustments				115	(115)
Common stock purchases	(90)	0	(5)		(85)	0	0
Distributions	(12)	$ 0	0		0	0	(12)
Other equity transactions	$ (4)		(5)				1
Balance (shares) at Jun. 30, 2018	77	77
Balance at Jun. 30, 2018	$ 28,304	$ 0	$ 6,358		$ 23,976	$ (1,665)	$ 129
Long-term income tax receivable	$ (494)			$ (494)