Income Taxes (Reconciliation of Beginning and Ending Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of year	$ 66	$ 169	$ 158
Additions based on tax positions related to the current year	0	0	15
Additions for tax positions of prior years	22	129	29
Reductions for tax positions due to lapse of statutes of limitations	0	(4)	(4)
Reductions for tax positions of prior years	(1)	(208)	(28)
Settlements	(2)	(20)	(1)
Balance at end of year	$ 85	$ 66	$ 169

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of unrecognized tax benefits.

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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