Other Comprehensive Income (Loss) - Textual (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Pension plan net loss [Member]
Accumulated Other Comprehensive Income [Line Items]
Pension and other postretirement benefit plans net gain (loss), cost (credit) in AOCI	$ 3,500	$ 1,700
Other postretirement benefit plan net loss [Member]
Accumulated Other Comprehensive Income [Line Items]
Pension and other postretirement benefit plans net gain (loss), cost (credit) in AOCI	228	80
Pension plan prior service cost credit [Member]
Accumulated Other Comprehensive Income [Line Items]
Pension and other postretirement benefit plans net gain (loss), cost (credit) in AOCI	473	559
Other Postretirement Benefit Plan Prior Service Cost [Member]
Accumulated Other Comprehensive Income [Line Items]
Pension and other postretirement benefit plans net gain (loss), cost (credit) in AOCI	$ 257	$ 331