Recast 2017 and 2016 Financial Information (Details 4) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	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	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	$ 8,187				$ 7,132				$ 8,187	$ 7,132	$ 5,363
Net Income (Loss) Attributable to Parent	356	$ 1,244	$ 789	$ 840	672	$ 750	$ 677	$ 770	3,229	2,869	2,043
Other comprehensive loss, net of tax									(74)	(46)	(113)
Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent					7,048					7,048	5,259
Net Income (Loss) Attributable to Parent										2,015	2,200
Other comprehensive loss, net of tax										828	(226)
Adjustments for change to Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Period Benefit (Cost) [Member] | Adjustments for Change in Accounting Principle [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent					0					0	0
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures									0
Stock Repurchased and Retired During Period, Value									0
Net Income (Loss) Attributable to Parent	(394)	$ 100	$ 100	$ 101	525	$ 107	$ 122	$ 120	(93)	874	(113)
Dividends, Common Stock									0
Other comprehensive loss, net of tax									93	(874)	113
Accounting Standards Update 2014-09 [Member] | Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent					84					84	104
Net Income (Loss) Attributable to Parent										(20)	(44)
Other comprehensive loss, net of tax										0	0
Accounting Standards Update 2017-07 [Domain] | Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Income (Loss) Attributable to Parent										0	0
Other comprehensive loss, net of tax										0	0
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	8,068				6,913				8,068	6,913	5,141	$ 5,329
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures									(6)	(39)	(50)
Stock Repurchased and Retired During Period, Value									(1,225)	(371)	(1,548)
Net Income (Loss) Attributable to Parent										2,869	2,043
Dividends, Common Stock									(822)	(687)	(633)
Retained Earnings [Member] | Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent					11,548					11,548	10,630	10,661
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures										(39)	(50)
Stock Repurchased and Retired During Period, Value										(371)	(1,548)
Net Income (Loss) Attributable to Parent										2,015	2,200
Dividends, Common Stock										(687)	(633)
Retained Earnings [Member] | Adjustments for change to Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Period Benefit (Cost) [Member] | Adjustments for Change in Accounting Principle [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	(5,897)				(4,719)				(5,897)	(4,719)	(5,593)	(5,480)
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures										0	0
Stock Repurchased and Retired During Period, Value										0	0
Net Income (Loss) Attributable to Parent										874	(113)
Dividends, Common Stock										0	0
Retained Earnings [Member] | Accounting Standards Update 2014-09 [Member] | Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent					84					84	104	148
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures										0	0
Stock Repurchased and Retired During Period, Value										0	0
Net Income (Loss) Attributable to Parent										(20)	(44)
Dividends, Common Stock										0	0
AOCI Attributable to Parent [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	(52)				1				(52)	1	47	160
Other comprehensive loss, net of tax									(74)	(46)	(113)
AOCI Attributable to Parent [Member] | Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent					(4,718)					(4,718)	(5,546)	(5,320)
Other comprehensive loss, net of tax										828	(226)
AOCI Attributable to Parent [Member] | Adjustments for change to Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Period Benefit (Cost) [Member] | Adjustments for Change in Accounting Principle [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	$ 5,897				4,719				$ 5,897	4,719	5,593	5,480
Other comprehensive loss, net of tax										(874)	113
AOCI Attributable to Parent [Member] | Accounting Standards Update 2014-09 [Member] | Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent					$ 0					0	0	$ 0
Other comprehensive loss, net of tax										$ 0	$ 0