Income Taxes (Unrecognized Tax Benefits Information) (Details 4) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits, net of federal tax benefits, that would impact the effective tax rate	$ 58	$ 46	$ 57
Increase (decrease) in interest and penalties	0	43	3
Payable related to accrued interest and penalties	8	8
Reconciliation of gross unrecognized tax benefits (expense)
Beginning balance	115	161	242
Additions based on tax positions related to the current year	16	15	18
Additions for tax positions of prior years	3	33	48
Reductions for tax positions of prior years	(57)	(87)	(147)
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	(1)	(7)	0
Ending balance	76	$ 115	$ 161
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross amount of unrecognized tax benefits due to resolution of IRS examinations	20
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in gross amount of unrecognized tax benefits due to resolution of IRS examinations	$ 30