Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2018	Sep. 30, 2017	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Unrecognized Tax Benefits	$ 1,066		$ 1,066				$ 1,056
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	986		986				975
Incremental tax liability asserted by IRS	$ 1,162		$ 1,162
Reported tax rate	11.20%	45.90%	(152.40%)	68.90%
Net tax expense/benefits related to interest and penalties	$ 13	$ 11	$ 35	$ 32
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 554		$ 554				$ 500
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						$ 758