Employee Benefits - Schedule of changes in Level 3 fair value for U.S. Pension Plans (Details) (U.S. [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Change in fair value of plan assets
Balance at the beginning of the period			$ 1,631
Actual return on plan assets:
Balance at the end of the period	2,036	1,855	1,631
Significant Unobservable Inputs (Level 3) [Member]
Change in fair value of plan assets
Balance at the beginning of the period	266	262
Actual return on plan assets:
Relating to assets still held at the end of the year	32	26
Relating to assets sold during the year	5	4
Purchases, sales and settlements—net	321	(26)
Transfer in/(out) of Level 3	0	0
Balance at the end of the period	$ 624	$ 266