Equity - Common Stock and Unit Issuances and Repurchases (Details) $ / shares in Units, $ in Billions			12 Months Ended
	Feb. 13, 2017	Apr. 02, 2015 USD ($)	Dec. 31, 2016 item $ / shares shares	Dec. 31, 2015 $ / shares shares	Dec. 31, 2014 shares
Equity
Minimum number of additional classes or series of common stock that the Board is authorized to reclassify from excess common stock			1
Exchange of limited partner units, (in shares) | shares			5,020,919	489,291	70,291
Period common stock is authorized to repurchase		24 months
Extension period common stock is authorized for repurchase	2 years
Shares repurchased (in shares) | shares			1,409,197	1,903,340
Average share price repurchased (in dollars per share) | $ / shares			$ 181.14	$ 180.19
Class B common stock
Equity
Common Stock, Shares, Outstanding | shares			8,000	8,000
Number of voting trusts which are subject to outstanding shares common stock			2
Common Stock
Equity
Number of votes entitled per share to holders of common stock			1
Limited Partners
Equity
Exchange of limited partner units, (in shares) | shares			5,020,919
Number of limited partners who received common stock			14
Maximum
Equity
Common stock authorized for repurchase | $		$ 2.0
Maximum | Class B common stock
Equity
Number of members of board of directors elected under entitlement of right			4