Employee Benefit Plans Employee Benefit Plans - Level 3 Rollforward (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Pension [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value, end of year	$ 1,146		$ 1,171		$ 1,012
Pension [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value, end of year	70	[1]	86	[1]
Pension [Member] | Limited Partnership Interests [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value, end of year	70	[2]	86	[2]
Pension [Member] | Limited Partnership Interests [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value, beginning of year	86	[1],[2]	96		71
Actual return on plan assets still held	(1)		16		7
Purchases, sales, distributions and settlements	(15)		(26)		18
Plan assets at fair value, end of year	70	[1],[2]	86	[1],[2]	96
Other Postretirement [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value, end of year	482		486		424
Other Postretirement [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value, end of year	5	[1]	6	[1]
Other Postretirement [Member] | Limited Partnership Interests [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value, end of year	5	[2]	6	[2]
Other Postretirement [Member] | Limited Partnership Interests [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value, beginning of year	6	[1],[2]	7		6
Actual return on plan assets still held	0		1		0
Purchases, sales, distributions and settlements	(1)		(2)		1
Plan assets at fair value, end of year	$ 5	[1],[2]	$ 6	[1],[2]	$ 7

[1] Refer to Note 12 for additional discussion regarding the three levels of the fair value hierarchy.

[2] Limited partnership interests include several funds that invest primarily in buyout, growth equity, venture capital and real estate.