Commitments and Contingencies - Narrative (Details) $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2016 claims lawsuit	Dec. 31, 2003 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jan. 31, 2016 employee	Aug. 30, 2015 shareholder employee	Dec. 31, 2013 USD ($)
Loss Contingencies [Line Items]
Sale of equity investment in Rock-McGraw, Inc., percentage		45.00%
Proceeds from the disposition of equity investment in Rock-McGraw		$ 382
Pre-tax gain from Sale of equity investment in Rock-McGraw		131
After-tax gain from Sale of equity investment in Rock-McGraw		58
Pre-tax gain pursuant to sale-leaseback accounting rules		212
After-tax gain pursuant to sale-leaseback accounting rules		$ 126
Deferred gain							$ 60
Gain amortized during year			$ 4	$ 21
Financial Crisis Litigation
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number | lawsuit	7
Shareholder Derivative Action
Loss Contingencies [Line Items]
Number of shareholders commencing punitive derivative action | shareholder						2
Number of former employees named as defendants | employee					9	3
Number of claims dismissed | claims	2