New Accounting Standards (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax benefit				$ 949	$ (266)	$ (276)
Impairment				905
Equity securities	$ 246			$ 246	275
Federal rate				35.00%
Deferred tax impact from the Tax Cut and Jobs Act				$ (1,322)
Scenario, Forecast [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Federal rate			21.00%
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax benefit					$ 8
Reclassification from additional paid-in capital		$ 3
Accounting Standards Update 2017-04 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impairment	905
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity securities	$ 110			$ 110
Accounting Standards Update 2018-02 [Member] | Scenario, Forecast [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax impact from the Tax Cut and Jobs Act			$ 600