Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Unrecognized Tax Benefits	$ 1,116		$ 1,116				$ 1,095
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	1,027		1,027				1,006
Incremental tax liability asserted by IRS	$ 1,162		$ 1,162
Reported tax rate	(60.30%)	47.80%	(10.10%)	97.00%
Net tax expense/benefits related to interest and penalties	$ 13	$ 13	$ 26	$ 23
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 612		$ 612				$ 572
Subsequent Event [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Litigation Settlement, Amount					$ 275
Potential Reduction In Unrecognized Tax Benefits Over Next Twelve Months As Result Of Concluding Certain Matters						$ 757