Income Taxes (Change in Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes In Unrecognized Tax Benefits
Beginning balance of unrecognized tax benefits	$ 503	$ 644	$ 297
Additions based on tax positions related to current year	0	1	18
Additions (reductions) for tax positions of prior years	(76)	(34)	343
Settlements	(1)	(17)	0
Lapse of statute of limitations	(1)	0	0
Unrecognized deferred tax benefits from acquisitions	1	(91)	(14)
Ending balance of unrecognized tax benefits	426	503	644
Federal
Unrecognized Tax Benefits That Would Have Impacted Effective Rate [Line Items]
Unrecognized tax benefit that would impact effective tax rate if recognized	422	497	631
State
Unrecognized Tax Benefits That Would Have Impacted Effective Rate [Line Items]
Unrecognized tax benefit that would impact effective tax rate if recognized	$ 3	$ 4	$ 11