v3.10.0.1
Debt - Senior Notes (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Jul. 31, 2014
Interest Rate Swap | Designated as Hedging Instrument | Fair Value Hedging            
Debt Instrument [Line Items]            
Derivative liability $ 2,400   $ 2,400     $ 2,400
Senior Notes            
Debt Instrument [Line Items]            
Redemption price, percentage, in the event of change of control     101.00%      
Interest expense 79 $ 83 $ 239 $ 225    
Fair value of long-term debt $ 9,100   9,100   $ 10,100  
Senior Notes | 2.500% Senior notes due 2018            
Debt Instrument [Line Items]            
Debt repaid     $ 750      
Coupon rate, fixed rate notes 2.50%   2.50%      
Senior Notes | 3.800% Senior notes due 2022            
Debt Instrument [Line Items]            
Coupon rate, fixed rate notes 3.80%   3.80%      
Senior Notes | 6.000% Senior notes due 2056            
Debt Instrument [Line Items]            
Coupon rate, fixed rate notes 6.00%   6.00%      
Redemption price, percentage     100.00%      
Senior Notes | 2.150% Senior notes due 2020            
Debt Instrument [Line Items]            
Coupon rate, fixed rate notes 2.15%   2.15%      
Senior Notes | 2.750% Senior notes due 2023            
Debt Instrument [Line Items]            
Coupon rate, fixed rate notes 2.75%   2.75%      
Senior Notes | 3.600% Senior notes due 2027            
Debt Instrument [Line Items]            
Coupon rate, fixed rate notes 3.60%   3.60%