Other Assets (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jul. 31, 2010	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Company limited partner holding interest, percentage	99.90%
Variable Interest Entity, Assets		$ 300		$ 315
Affordable Housing Tax Credits and Other Tax Benefits, Amount		9	$ 9
Unamortized investment balance classified as Other Assets		248		265
Maximum exposure to loss		$ 248		$ 265
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
General partner holding interest, percentage	0.10%