Income Taxes (Unrecognized Tax Benefit Changes) (Details) $ in Millions	Sep. 30, 2017 USD ($)
Minimum [Member]
Significant Change In Unrecognized Tax Benefits Is Reasonably Possible [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change	$ 30
Maximum [Member]
Significant Change In Unrecognized Tax Benefits Is Reasonably Possible [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change	435
Non-cash tax gain [Member]
Significant Change In Unrecognized Tax Benefits Is Reasonably Possible [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change	55
Non-cash interest gain [Member]
Significant Change In Unrecognized Tax Benefits Is Reasonably Possible [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change	$ 9