New Accounting Standards (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
AFS Equity securities		$ 246
Equity Securities, FV-NI	$ 112
Federal rate	21.00%	35.00%
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
AFS Equity securities		$ 246
Equity Securities, FV-NI		110
Cumulative effect of adoption	$ 1
Accounting Standards Update 2016-01 [Member] | Scenario, Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
AFS Equity securities		$ (136)
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from AOCI to retained earnings	$ 641