Significant Accounting Policies Common Stock Repurchase Program (Details) - USD ($) shares in Millions, $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 140
cumulative value of shares repurchased through stock repurchase program	$ 1,000
cumulative common stock repurchased through repurchase program	29.3
Stock Repurchased During Period, Value	$ 125	$ 160
Stock Repurchased During Period, Shares	1.8	2.7
January 2015 Accelerated Share Repurchase [Member]
Accelerated Share Repurchase - Cash Paid	$ 100
January 2015 Accelerated Share Repurchase [Member] | Shares received at settlement [Member]
Accelerated Share Repurchase - shares received at settlement	0.2
January 2015 Accelerated Share Repurchase [Member] | Initial share value [Member]
Accelerated share repurchase - initial share value	$ 80
January 2015 Accelerated Share Repurchase [Member] | Initial shares received [Member]
Accelerated share repurchase - initial shares received	1.1
January 2015 Accelerated Share Repurchase [Member] | Additional Paid-in Capital [Member]
Option Indexed to Issuer's Equity, Redeemable Stock, Redemption Requirements, Amount	$ 20
December 2014 Accelerated Share Repurchase [Member]
Accelerated Share Repurchase - Cash Paid			$ 75
December 2014 Accelerated Share Repurchase [Member] | Shares received at settlement [Member]
Accelerated Share Repurchase - shares received at settlement	0.2
December 2014 Accelerated Share Repurchase [Member] | Initial share value [Member]
Accelerated share repurchase - initial share value			$ 60
December 2014 Accelerated Share Repurchase [Member] | Initial shares received [Member]
Accelerated share repurchase - initial shares received			0.8
December 2014 Accelerated Share Repurchase [Member] | Additional Paid-in Capital [Member]
Option Indexed to Issuer's Equity, Redeemable Stock, Redemption Requirements, Amount			$ 15