Employee Postretirement Benefits (Pension Plan Assets of the Principal Plans Measured at fair value) (Details) - USD ($) $ in Millions | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 |
Defined Benefit Plan, Accumulated Benefit Obligation | $ 3,847 | $ 6,696 | |
Defined Benefit Pension Plans | | | |
Defined Benefit Plan, Benefit Obligation | 3,959 | 6,860 | $ 6,164 |
Fair value of plan assets | 3,508 | 5,914 | $ 5,567 |
Principal Plans | | | |
Defined Benefit Plan, Benefit Obligation | 3,295 | 6,312 | |
Defined Benefit Plan, Accumulated Benefit Obligation | 3,253 | 6,221 | |
Fair value of plan assets | 3,019 | 5,559 | |
Principal Plans | Fair Value, Inputs, Level 1 | | | |
Fair value of plan assets | 241 | 161 | |
Principal Plans | Fair Value, Inputs, Level 2 | | | |
Fair value of plan assets | 2,778 | 5,398 | |
Principal Plans | Fair Value, Inputs, Level 3 | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | U.S. Equity | | | |
Fair value of plan assets | 58 | | |
Principal Plans | U.S. Equity | Mutual and Pooled Funds | | | |
Fair value of plan assets | | 4 | |
Principal Plans | U.S. Equity | Fair Value, Inputs, Level 1 | | | |
Fair value of plan assets | 58 | | |
Principal Plans | U.S. Equity | Fair Value, Inputs, Level 1 | Mutual and Pooled Funds | | | |
Fair value of plan assets | | 4 | |
Principal Plans | U.S. Equity | Fair Value, Inputs, Level 2 | | | |
Fair value of plan assets | 0 | | |
Principal Plans | U.S. Equity | Fair Value, Inputs, Level 2 | Mutual and Pooled Funds | | | |
Fair value of plan assets | | 0 | |
Principal Plans | U.S. Equity | Fair Value, Inputs, Level 3 | | | |
Fair value of plan assets | 0 | | |
Principal Plans | U.S. Equity | Fair Value, Inputs, Level 3 | Mutual and Pooled Funds | | | |
Fair value of plan assets | | 0 | |
Principal Plans | International Equity | | | |
Fair value of plan assets | 30 | | |
Principal Plans | International Equity | Fair Value, Inputs, Level 1 | | | |
Fair value of plan assets | 30 | | |
Principal Plans | International Equity | Fair Value, Inputs, Level 2 | | | |
Fair value of plan assets | 0 | | |
Principal Plans | International Equity | Fair Value, Inputs, Level 3 | | | |
Fair value of plan assets | 0 | | |
Principal Plans | Non-U.S. Equity | Mutual and Pooled Funds | | | |
Fair value of plan assets | 67 | 106 | |
Principal Plans | Non-U.S. Equity | Fair Value, Inputs, Level 1 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | 1 | |
Principal Plans | Non-U.S. Equity | Fair Value, Inputs, Level 2 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 67 | 105 | |
Principal Plans | Non-U.S. Equity | Fair Value, Inputs, Level 3 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | International Bonds | Mutual and Pooled Funds | | | |
Fair value of plan assets | 1,236 | 1,438 | |
Principal Plans | International Bonds | Fair Value, Inputs, Level 1 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | International Bonds | Fair Value, Inputs, Level 2 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 1,236 | 1,438 | |
Principal Plans | International Bonds | Fair Value, Inputs, Level 3 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | U.S. securitized fixed income | | | |
Fair value of plan assets | | 6 | |
Principal Plans | U.S. securitized fixed income | Fair Value, Inputs, Level 1 | | | |
Fair value of plan assets | | 0 | |
Principal Plans | U.S. securitized fixed income | Fair Value, Inputs, Level 2 | | | |
Fair value of plan assets | | 6 | |
Principal Plans | U.S. securitized fixed income | Fair Value, Inputs, Level 3 | | | |
Fair value of plan assets | | 0 | |
Principal Plans | Cash and Cash Equivalents | | | |
Fair value of plan assets | 14 | 28 | |
Principal Plans | Cash and Cash Equivalents | Mutual and Pooled Funds | | | |
Fair value of plan assets | 34 | 175 | |
Principal Plans | Cash and Cash Equivalents | Fair Value, Inputs, Level 1 | | | |
Fair value of plan assets | 12 | 28 | |
Principal Plans | Cash and Cash Equivalents | Fair Value, Inputs, Level 1 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | 9 | |
Principal Plans | Cash and Cash Equivalents | Fair Value, Inputs, Level 2 | | | |
Fair value of plan assets | 2 | 0 | |
Principal Plans | Cash and Cash Equivalents | Fair Value, Inputs, Level 2 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 34 | 166 | |
Principal Plans | Cash and Cash Equivalents | Fair Value, Inputs, Level 3 | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | Cash and Cash Equivalents | Fair Value, Inputs, Level 3 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | U.S. government and municipals | | | |
Fair value of plan assets | 157 | 252 | |
Principal Plans | U.S. government and municipals | Mutual and Pooled Funds | | | |
Fair value of plan assets | 149 | | |
Principal Plans | U.S. government and municipals | Fair Value, Inputs, Level 1 | | | |
Fair value of plan assets | 141 | 71 | |
Principal Plans | U.S. government and municipals | Fair Value, Inputs, Level 1 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | | |
Principal Plans | U.S. government and municipals | Fair Value, Inputs, Level 2 | | | |
Fair value of plan assets | 16 | 181 | |
Principal Plans | U.S. government and municipals | Fair Value, Inputs, Level 2 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 149 | | |
Principal Plans | U.S. government and municipals | Fair Value, Inputs, Level 3 | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | U.S. government and municipals | Fair Value, Inputs, Level 3 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | | |
Principal Plans | U.S. corporate debt | | | |
Fair value of plan assets | 21 | 2,167 | |
Principal Plans | U.S. corporate debt | Mutual and Pooled Funds | | | |
Fair value of plan assets | 623 | 149 | |
Principal Plans | U.S. corporate debt | Fair Value, Inputs, Level 1 | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | U.S. corporate debt | Fair Value, Inputs, Level 1 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | U.S. corporate debt | Fair Value, Inputs, Level 2 | | | |
Fair value of plan assets | 21 | 2,167 | |
Principal Plans | U.S. corporate debt | Fair Value, Inputs, Level 2 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 623 | 149 | |
Principal Plans | U.S. corporate debt | Fair Value, Inputs, Level 3 | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | U.S. corporate debt | Fair Value, Inputs, Level 3 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | Multi-sector | Mutual and Pooled Funds | | | |
Fair value of plan assets | | 1 | |
Principal Plans | Multi-sector | Fair Value, Inputs, Level 1 | Mutual and Pooled Funds | | | |
Fair value of plan assets | | 1 | |
Principal Plans | Multi-sector | Fair Value, Inputs, Level 2 | Mutual and Pooled Funds | | | |
Fair value of plan assets | | 0 | |
Principal Plans | Multi-sector | Fair Value, Inputs, Level 3 | Mutual and Pooled Funds | | | |
Fair value of plan assets | | 0 | |
Principal Plans | Global equity | Mutual and Pooled Funds | | | |
Fair value of plan assets | 630 | 1,186 | |
Principal Plans | Global equity | Fair Value, Inputs, Level 1 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 0 | 0 | |
Principal Plans | Global equity | Fair Value, Inputs, Level 2 | Mutual and Pooled Funds | | | |
Fair value of plan assets | 630 | 1,186 | |
Principal Plans | Global equity | Fair Value, Inputs, Level 3 | Mutual and Pooled Funds | | | |
Fair value of plan assets | $ 0 | 0 | |
Principal Plans | Insurance Contract | | | |
Fair value of plan assets | | 29 | |
Principal Plans | Insurance Contract | Fair Value, Inputs, Level 3 | | | |
Fair value of plan assets | | 0 | |
Principal Plans | Equity - Held Through Mutual and Pooled Funds | Fair Value, Inputs, Level 1 | | | |
Fair value of plan assets | | 29 | |
Principal Plans | Equity - Held Through Mutual and Pooled Funds | Fair Value, Inputs, Level 2 | | | |
Fair value of plan assets | | 0 | |
U.S. Equity | Equity - Assets Held Directly | | | |
Fair value of plan assets | | 18 | |
U.S. Equity | Equity - Assets Held Directly | Fair Value, Inputs, Level 1 | | | |
Fair value of plan assets | | 18 | |
U.S. Equity | Equity - Assets Held Directly | Fair Value, Inputs, Level 2 | | | |
Fair value of plan assets | | 0 | |
U.S. Equity | Equity - Assets Held Directly | Fair Value, Inputs, Level 3 | | | |
Fair value of plan assets | | $ 0 | |