Restructuring Charges (Schedule of restructuring charges) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance			$ 17
Charged to Costs and Expenses	$ 19	$ 2	19	$ 4
Payments and Other			(15)
Ending Reserve Balance	21		21
Branch closure charges
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance			16
Charged to Costs and Expenses			3
Payments and Other			(3)
Ending Reserve Balance	16		16
Severance and other
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance			1
Charged to Costs and Expenses			16
Payments and Other			(12)
Ending Reserve Balance	5		5
Closed Restructuring Programs
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance			17
Charged to Costs and Expenses			0
Payments and Other			(3)
Ending Reserve Balance	14		14
Closed Restructuring Programs | Branch closure charges
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance			16
Charged to Costs and Expenses			0
Payments and Other			(2)
Ending Reserve Balance	14		14
Closed Restructuring Programs | Severance and other
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance			1
Charged to Costs and Expenses			0
Payments and Other			(1)
Ending Reserve Balance	0		0
NES/Project XL Restructuring Program
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance			0
Charged to Costs and Expenses			19
Payments and Other			(12)
Ending Reserve Balance	7		7
NES/Project XL Restructuring Program | Branch closure charges
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance			0
Charged to Costs and Expenses			3
Payments and Other			(1)
Ending Reserve Balance	2		2
NES/Project XL Restructuring Program | Severance and other
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance			0
Charged to Costs and Expenses			16
Payments and Other			(11)
Ending Reserve Balance	$ 5		$ 5