Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reduction in net deferred tax liability due to change of corporate income tax rate	$ 495
Deferred tax benefit due to tax rate change	67.80%	(0.00%)	(0.00%)
Excess tax benefit, amount	$ 7
Excess tax benefit percent	1.00%
Income taxes paid, net	$ 18	$ 2	$ 0
Retained Earnings | Accounting Standards Update 2018-02 | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to reclassify certain tax effects from AOCI to retained earnings	(492)	0	0
Accumulated Other Comprehensive Income | Accounting Standards Update 2018-02 | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to reclassify certain tax effects from AOCI to retained earnings	$ 492	$ 0	$ 0