2018 Impact of Accounting Method Change (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
Other comprehensive loss, net of tax									(74)	(46)	(113)
Net Income (Loss) Attributable to Parent	356	$ 1,244	$ 789	$ 840	672	$ 750	$ 677	$ 770	3,229	2,869	2,043
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
Other comprehensive loss, net of tax									93	(874)	113
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
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures									0
Method Prior to change to Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Period Benefit (Cost) [Member] [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other comprehensive loss, net of tax									(167)
Stock Repurchased and Retired During Period, Value									1,225
Net Income (Loss) Attributable to Parent									3,322
Dividends, Common Stock									822
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures									(6)
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
Impact from adoption of ASU 2018-02 and ASU 2016-01									(21)	0	0
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
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures									(6)	(39)	(50)
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)
Impact from adoption of ASU 2018-02 and ASU 2016-01									(1,085)
Stock Repurchased and Retired During Period, Value										0	0
Net Income (Loss) Attributable to Parent										874	(113)
Dividends, Common Stock										0	0
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures										0	0
Retained Earnings [Member] | Method Prior to change to Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Period Benefit (Cost) [Member] [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	13,965				11,632				13,965	11,632
Impact from adoption of ASU 2018-02 and ASU 2016-01									1,064
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
Impact from adoption of ASU 2018-02 and ASU 2016-01									21	0	0
Other comprehensive loss, net of tax									(74)	(46)	(113)
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
Impact from adoption of ASU 2018-02 and ASU 2016-01									1,085
Other comprehensive loss, net of tax										(874)	$ 113
AOCI Attributable to Parent [Member] | Method Prior to change to Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Period Benefit (Cost) [Member] [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	$ (5,949)				$ (4,718)				(5,949)	$ (4,718)
Impact from adoption of ASU 2018-02 and ASU 2016-01									$ (1,064)