Change in Accounting Principles (Details) - USD ($) $ in Millions		Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Liability		$ 967
Accumulated Other Comprehensive Income , Net of Tax		(5,914)		$ (6,063)
Retained Earnings (Accumulated Deficit)		35,534		34,010
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated Other Comprehensive Income , Net of Tax				(6,063)
Retained Earnings (Accumulated Deficit)				$ 34,010
Accounting Standards Update 2016-02 (Topic 842) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Liability		$ 967
Accounting Standards Update 2016-02 (Topic 842) [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset			$ 998
Operating Lease, Liability			998
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated Other Comprehensive Income , Net of Tax			(6,103)
Retained Earnings (Accumulated Deficit)			34,050
Accounting Standards Update 2018-02 [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated Other Comprehensive Income , Net of Tax	[1]		(40)
Retained Earnings (Accumulated Deficit)	[1]		$ 40

[1] For additional information regarding the impact of the adoption of ASU No. 2018-02, see Note ##NAOCI—Accumulated Other Comprehensive Loss.