Employee Benefit Plans - Schedule of Benefits Measured at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	$ 10,030	$ 10,351
Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	2,083	752
Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	2,753	5,001
Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	5,194	4,598
Equities and equity-related instruments
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	2,218	2,185
Equities and equity-related instruments | Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	2,067	699
Equities and equity-related instruments | Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	50	1,486
Equities and equity-related instruments | Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	101	0
Sovereign fixed income
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	86	0
Sovereign fixed income | Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	8	0
Sovereign fixed income | Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	78	0
Sovereign fixed income | Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Credit-related fixed income
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	858	594
Credit-related fixed income | Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Credit-related fixed income | Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	761	470
Credit-related fixed income | Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	97	124
Other fixed income
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	174	635
Other fixed income | Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	8	18
Other fixed income | Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	143	617
Other fixed income | Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	23	0
Private equity
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	1,030	1,213
Private equity | Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Private equity | Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Private equity | Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	1,030	1,213
Real assets
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	635	663
Real assets | Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Real assets | Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Real assets | Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	635	663
Hedge Funds
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	2,990	2,245
Hedge Funds | Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	31
Hedge Funds | Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	19	0
Hedge Funds | Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	2,971	2,214
Cash equivalents
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	1,700	2,432
Cash equivalents | Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	4
Cash equivalents | Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	1,700	2,428
Cash equivalents | Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Other
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	339	384
Other | Level 1
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Other | Level 2
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	2	0
Other | Level 3
Defined Benefit Plan, Funded Status of Plan
Defined Benefit Plan, Fair Value of Plan Assets	$ 337	$ 384