Other Assets (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jul. 31, 2010	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Company limited partner holding interest, percentage	99.90%
Tax credits, reduction to income tax expense		$ 8	$ 9
Unamortized investment balance classified as Other Assets		179		$ 196
Maximum exposure to loss		$ 179		$ 196
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
General partner holding interest, percentage	0.10%