Summary of Significant Accounting Policies - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) line_of_business	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Accounting Policies [Abstract]
Number of lines of business | line_of_business	2
Debt issuance cost	$ 37
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total shareholders’ equity	(21,103)	$ (21,328)	$ (20,248)	$ (20,825)
Retained Earnings
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total shareholders’ equity	$ (16,049)	$ (14,737)	$ (13,265)	(11,707)
Cumulative Adjustment for Incorrect Revenue Recognition
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Recognition period	18 years
Cumulative amount of revenue recognized	$ 240
Correction | Cumulative Adjustment for Incorrect Revenue Recognition | Retained Earnings
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total shareholders’ equity				$ 44