Business, Basis of Presentation and Summary of Significant Accounting Policies (New Accounting Pronouncements) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ 11,631	$ 6,911		$ 1,722	$ 2,854	$ 5,634	$ 7,427
Retained Earnings (Accumulated Deficit)	31,209			$ 28,926
Operating Lease, Right-of-Use Asset	1,494
Operating Lease, Right-of-Use-Liability	$ 1,660
Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax			$ 18
Retained Earnings (Accumulated Deficit)			(18)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained Earnings (Accumulated Deficit)			95
Operating Lease, Right-of-Use Asset			1,500
Operating Lease, Right-of-Use-Liability			$ 1,700